I may as well state it up front: I love hotels to the point of obsession. Sure, everyone gets a bit misty-eyed over white, fluffy dressing gowns, but I can well up at the sight of the fancy folds at the end of a loo roll after the room's been cleaned. I've hoarded hotel pens; lurked in the lobbies of places I'm not even staying in; even paid through the nose for a glass of fizzy water just to sit in the legendary Dukes' hotel bar.

Yet despite my childlike awe at these self-contained worlds in which your every whim is catered for, there is one aspect of hotels that – until recently at least – never really grabbed me: the restaurant. For, where the rest of the building oozed charisma and attention to detail, the dining room of a hotel invariably had as much charm and culinary potential as a school canteen.

So I approached this brief with caution. Of course, I knew some hotel restaurants were peerless – The Savoy, The Ritz – but they were the luminaries. They weren't representative of Britain's contemporary hotel restaurant scene any more than Westminster Cathedral is of its architecture. I needed Ollie Dabbous, now of Henrietta; Nuno Mendes of Chiltern Firehouse; Frédéric Peneau, the chef whose recently opened Serge et le Phoque at the Mandrake hotel has brought rave reviews rolling in.

Initially Peneau throws me a curve ball: "Serge et le Phoque is not a hotel restaurant," he insists. "After Chateaubriand," – his defining restaurant which spearheaded the neo-bistro movement back in the 1990s – "I was scared to open another 'bistronomique' or 'gastronomique' restaurant in France." So he opened a 'fast food' gourmand kebab shop, Grillé in Paris, and at the same time opened Serge et le Phoque on the other side of the world in Hong Kong. Serge et le Phoque in the Mandrake was born when Rami Fustok, his future business partner, stopped by and "fell in love with the friendly atmosphere and our high standard of food – good but also relaxed, you know?" Peneau continues. "We shared our ideas – Rami's for the hotel and mine for the restaurant – and they aligned."

hotel dining rooms used to have as much charm as a canteen

So a restaurant in a hotel then, as opposed to a 'hotel restaurant'. This sounds suspiciously like semantics – but Peneau's aversion proved my point about the term's connotations. "I think for a long while hotel restaurants were seen as a service that could maximise a hotel's revenue from guests, without making much effort," explains Luke Holder, head chef of Hartnett Holder & Co at the New Forest's Lime Wood hotel.

Holder's business partner is none other than Angela Hartnett, the Michelin-starred chef of Murano and formerly of the Connaught hotel. "When we arrived at Lime Wood the philosophy of the restaurant was not 'this is a place for local people' but 'this is a fine-dining restaurant for our guests, and locals only on special occasions.' The biggest focus for us, taking it over, was Monday to Thursday lunchtimes", because it's lunch, he continues – the business dinners, the yummy mummies, the darling dads – that is the biggest indicator of how integrated you are into the community.

In five years, they've tripled it. "It used to be five to 15 daily. Now it's 40 to 60," Holder says proudly. It's aspirational, but accessible. "It's simple Italian cooking, which everyone loves, but the fact that Angela has three Michelin stars to her name and has worked in Italy adds credibility to that simplicity."

Instead of relying on the hotel guests, Hartnett and Holder struck out for the harder, deeper waters of the residents of Lyndhurst and surrounding towns. "We made a real effort to appeal to the local market. Using local suppliers has also helped that. We have the same pricing as our good local gastropubs – but equally price isn't always a factor. It's value," he continues. Ten years ago, your average diner had the choice between Michelin-starred hotel joints or pubs and chain restaurants. By offering an affordable restaurant "with its own identity where quality is guaranteed and the menu's not regurgitated," Lime Wood latched onto what was the burgeoning middle ground.

For hotel restaurants, this has been crucial. Marcus Wareing's stellar career has charted their evolution like no other, and it's one of the first points he makes when we meet at the Berkeley hotel. "When I first moved to London, hotel restaurants were fine dining rooms – places for power lunches and dress-up dinner dances. Then all these talented chefs started popping up on high streets, making great food accessible, and the hotels had to start upping their game."

I look around: talking middle-ground dining with a Michelin-starred chef in his eponymous restaurant feels incongruous, especially having just scaled the five-star marble steps of the Berkeley. Yet while Wareing is first and foremost a chef, he is also the owner of three iconic restaurants, two of which are in hotels; and his feel for the ingredients of their success could not be more sound.

Of course, he agreed there were the luminaries that couldn't really change, and shouldn't change. "The Ritz never does anything different. That's why you go there. It's like Buckingham Palace."

For the most part, though, come the turn of the millennia, hotel restaurants found themselves competing not just with the hot new local talent, but on a global stage. "When I first came to London, the only place to eat out was hotels, and it was very standardised: French, nouvelle cuisine, white plates with very little on them. Then the Roux brothers opened Le Gavroche and brought proper food to the high street, inspiring a whole new generation." Waring was one of them; the other Gordon Ramsay, whose arrival at Claridge's heralded a sea of change in hotel fare.

"That's when the revolution really started," Wareing says firmly. "In 2001, when Gordon went to Claridge's." With him came the combined, Michelin star-spangled influence not just of Albert Roux, but Pierre Koffmann, Marco Pierre White and Joël Robuchon. He'd run his own restaurant, Restaurant Gordon Ramsay, earning three stars in his own right by the time he even picked up one of hospitality's most historic mantles. By 2005, Gordon Ramsay at Claridge's had a Michelin star, and was making the hotel an annual profit of £2 million. Don't let the hype of the Henrietta blind you to the fact that "what Ollie's doing is really not very different to what Gordon was doing – what I, and Jason Atherton were doing – 10 or 15 years ago."

"Of course, it's a new generation," Wareing acknowledges, "but we're still here doing it." The focus on great produce, the global outlook, more accessible pricing – none of the elements which make restaurant food what it is today would have come about without his generation's hard work.

hotels have had to start upping their game

Naturally there are those who argue, with some justification, that the drive to bring more fun and informality to hotel food is a mark of the "second wave of great chefs in hotel restaurants," says Gavin Couper, food and beverage manager at One Aldwych in Covent Garden. "There's a distinct absence of stuffiness and pretension." In 2016 they invited Eneko Atxa to bring his Michelin-starred Basque cuisine to their tables. "We wanted to introduce Londoners to Basque cooking that's accessible yet still authentic – food that is different but relatable," Couper continues. "Hotel restaurants, just like standalone restaurants, need to be relevant to London and relevant to today's informal eating culture."

Over in a beautifully restored former fire station in Marylebone, Nuno Mendes agrees with him. Even now, five years after the hype of its opening, Chiltern Firehouse remains one of the hottest watering holes in London. "I think that hotels here have been very classic in the past, and there is a certain stiffness about the experience there. They are not too street-conscious," he explains. Chiltern Firehouse, meanwhile, reads like the greatest hits of restaurant trends post 2013. Slick cocktails, chefs cooking in an open kitchen, copper bar tops, burrata, ceviche; if, as Mendes suggests, part of the secret to a successful hotel restaurant is "being in touch and engaged with trends and local guests" then he's nailed it. But if that's the case, then why are Michel Roux Jr, Marcus Wareing and Hélène Darroze – all of whom serve French food in fine, five-star dining rooms – doing so remarkably well?

The answer, for Hélène Darroze, is quality: "Of the food, the service, the design, everything. That's true of everywhere of course," she tells me, on the phone from her clattering, clinking, bustling kitchen, "but we are part of the Connaught hotel." Like the Langham, Claridge's and the Berkeley, there is a venerable history here with which the restaurant is inextricably linked. "There's a sense of tradition, which we had to take on board," she continues. As Wareing points out, "You couldn't come through this door and it be all exposed brickwork. There has to be a synergy." He gestures to the smart leather banquettes and the deep pile carpet. "It is a five-star hotel."

Five star is not the same as stuffy. When Holder and Hartnett took over the kitchen at Lime Wood, one of their first moves was to tone down the opulence. "It used to be a very intimating space to walk into, especially on a weekday lunchtime," recalls Holder. A coffee machine, some decent music and a bar area later, and it's a great atmosphere, rather than the cold sound of cutlery, that bounces off the walls. For all that the food has improved, Nuno Mendes' observation that hotel restaurants have tended to "miss the sexy, fun element that a standalone restaurant offers" still has validity; some hotel restaurants, such as Eneko at One Aldwych and Shaun Rankin's Ormer at Flemings in Mayfair have gone so far as to build separate entrances for their dining rooms to help lend them an air of individuality.

"It has to have its own identity, it's own branding – and it helps to have its own street entrance," says Rankin. Wareing and Darroze beg to differ. "I love entering hotels – even hotel toilets!" Darroze tells me, laughing. "Who doesn't like being welcomed by the doorman into a beautiful hotel?" Wareing exclaims, gesturing across the hall toward the Berkeley's shimmering lobby.

That said, these chefs are the first to acknowledge the need to temper the grandeur of an iconic hotel with a recognition of the prevailing zeitgeist: informal dining. "The entire Eneko London operation is quality-driven but not stuffy, from the design (by award-winning exhibition designers Casson Mann) to the style of food – informal modern Basque," explains Couper.

When Wareing gave Marcus a facelift in 2014, he described scrapping the stuffiness as his "number-one priority"; for Roux, who is about to open his second incarnation of Roux at the Landau when I speak to him, it has all been about "making it more convivial and accessible." They are introducing a 'cheese cave'; rich displays of ham and seafood; a kitchen 'island' at which diners can sit and watch the chefs at work. "It will be an immersive experience," Roux enthuses. The white tablecloths will remain in place, as will the chandeliers and perfect arch windows, but the new Landau will be led by the produce, and the experience of the customer.

Of course, none of these transformations would have been complete without a menu change, especially in those hotels where French cuisine is de rigueur. At Marcus, the pre-2014 ten ingredient dishes went the same way as the dark burgundy carpet. At the Landau, they are "paring back and returning to the true essence of French cooking" – for parallel to, and inextricably linked with, the revolution in British hotel food, has been a revolution in French gastronomy.

Getting a celebrity chef makes it easier to attract customers

"It stagnated for many years because there was just too much ego," says Roux – "but it's really buzzy at the moment. All these young French chefs getting rid of the excess garnishes and concentrating on great produce." For the grand dames of London's hotel restaurant scene, one of the major challenges has been appealing to a new crowd of locals and visitors without alienating the old reliables. Retaining a fine-dining offering which reflects these changes in French cooking has allowed veterans to be pacified, but not at the expense of modernity or flavour.

In some respects, the story behind the success of hotel restaurants in the last ten years is the story of all restaurants. They're sourcing quality produce – British where possible – from small, select suppliers and making them the centrepiece: "Where once you had to go through the markets – Billingsgate, Smithfield and so on – these days you can go straight to the fisherman or the farmer," says Wareing.

Meanwhile the introduction of more and more exotic ingredients has brought an extra dimension to the pantry, and the internet a wealth of culinary inspiration. "We don't have to wait for something to come to London," he continues. "We can look around the world through our phones."

Food is fashionable now. The ease with which chefs move between restaurant kitchen and television sets has brought them into "a different marketplace," says Rankin, whose own appearances on Masterchef and Saturday Kitchen have worked wonders for Ormer. "You've got an audience of six million people." Some chefs I speak to play down the idea that a name makes a difference – "Bollocks to that!" exclaims Perneau of Serge Le Phoque. "The food and wine and atmosphere should speak for itself" – but Rankin is comfortable admitting that "when restaurants get celebrity chefs, it makes it easier to attract customers."

And yet there is an irreducible difference between a restaurant in a hotel, and one that's independent. Regardless of whether, like Roux and Mendes, you see a hotel as "a restaurant with bedrooms", or like Wareing as a "bedroom with different elements attached to it," the marriage of food and accommodation adds a layer of complexity that makes the success of hotel restaurants even more remarkable.

"You don't stay all night in a hotel any more," Rankin points out. "You land and you are immediately looking at where to go next, where to eat, and what to see. Hotel restaurants needed to get on board with that." The worst kissed goodbye to all but tired business people and the least adventurous of guests; the best welcomed local residents, the guests of other hotels ("the concierges work together," Rankin smiles. "So the hotel restaurants share clientele") and yours truly: fully converted, and excited at the prospect of comparing all the different napkin origami.