Nicholas Lander at Nahm and Mju

In a recent 'Letter from America' on BBC radio the veteran broadcaster Alastair Cooke used the phrase 'chefs follow money' to describe what happened when the Kennedys swept into the White House in 1960 and a renowned French chef, René Verdon, followed in their wake.

Cooke could just as easily have been describing the current London restaurant scene. Over the past five years chefs from France, Italy, the US and Ireland have flown in to satisfy the capital's diners, more knowledgeable and until recently better off than ever before, and a plethora of keen investors (perhaps another disappearing group).

With the arrival of David Thompson and Tetsuya Wakuda, formerly neighbours in Sydney, Australia, to take over the respective kitchens at what is now Nahm in The Halkin and Mju in The Millennium hotels, this process may have reached its most illogical conclusion.

Both chefs quite rightly achieved fame and recognition for their culinary skills in Sydney. After a chance holiday in Thailand, Thompson became besotted with the flavours, textures and heritage of Thai food, went on to learn from Khun Sombot Janpahetchara, an elderly woman whom Thompson lovingly described as a 'dragon' when it came to technique, all that she could teach him and subsequently opened the acclaimed Darley Street Thai. Tetsuya, arrived in Australia from Japan 20 years ago and worked alongside the highly influential Tony Bilson before opening his own restaurant Tetsuya's, where some of the dishes can be exceptional but the formula of a set menu dictated by the kitchen tends to limit rather than enhance an evening out. In inappropriate hands, as at Mju, this can be disastrous.

I would advise anyone who is excited by Thai food to save up and visit Nahm. Thompson is an exceptionally serious and accomplished chef who has come over here because he has appreciated what Vong and Nobu have done for French/Thai and modern Japanese food and because of Britain's long association with the spicier food of the Indian sub-continent. The time is ripe, he believes, to do the same for Thailand's more traditional food.

And in a quite short space of time, despite major obstacles such as the lack of a ready supply of fresh coconut milk which is an integral part of Thai food, Thompson is achieving this with dishes such as minced prawns and chicken in palm sugar; a salad of crisp salted trout and corn peppers; a jungle curry of monkfish and coriander that was as hot as anything I have ever eaten followed fortunately by cooling poached mangosteens.

But for Thompson and those who would enjoy his food there are two ancillary obstacles bigger than the sourcing of any one ingredient. The first is whether this type of cooking can ever justify the ridiculously high prices the hotel have put on his menu particularly now that good value Thai food is ubiquitous. The second is perhaps even more basic. Thai food is fun, an integral, democratic part of the nation's culture, yet here thanks to what has been an expensive redesign it is has been put in a distinctly cool setting. The room lacks warmth but those who can currently afford to eat there are the most unlikely to supply it.

But at least Nahm, with Thompson a physical presence in the kitchen with antennae only too aware of how much better his cooking will become in time, is an addition to London's culinary repertoire. The only memorable item on our bill for £179.45 for dinner for two at Mju was a slightly underpriced bottle of Rousseau's Clos de la Roche 1995 at £55.

Tetsuya's input is a head chef, Chris Behre, several Australian waiters who have worked for him before and a nine-course, no choice, ominously undated menu. The hotel provides the low-ceilinged dining room and the smartly besuited men to open and close the main doors, but there is no synergy here. Mju conspicuously lacks personality.

And its staff lack training. Accidents happen too frequently around the room and a lack of food knowledge and sensitivity are pervasive. For example, a second course of oysters with a ginger dressing is listed on the menu as optional but is in fact extra.

This could be forgiven if the kitchen delivered but it failed time and time again during our recent dinner. A trio of cold soups, cauliflower, avocado and aubergine, looked the same and tasted equally insipid despite the caviar topping; a confit of wild salmon was bland whilst the dressing on its accompanying salad was too sweet and too cold (a fault common to several of the dishes). Ending the meal with two over-sweet, dairy-based desserts – a vanilla and blue cheese bavarois followed by a sickly dumbed down version of floating islands – seemed singularly out of keeping with the rest of the meal.

Ironically, it was whilst staying on Sloane Street more than a decade ago that American entrepeneur, Bill Kimpton, who sadly died earlier this year, first appreciated what was needed to make restaurants within hotels a success. As well as any restaurant's essential four criteria – excellent food and service, motivated staff and value for money – Kimpton's diagnosis, which allowed him to go on and successfully open hotel restaurants up and down the West Coast, was that a separate entrance was crucial to give the restaurant its own identity and personality (which Vong and Nobu both have) and, somewhat incongruously in California, working fireplaces by the entrance to generate warmth.

The owners and management of these two hotels have failed to appreciate these increasingly important subtleties. Instead, they have hired Thompson and Tatsuya as 'trophy chefs', using the corporate chequebook to acquire these additions to their hotels' assets. Thompson, in particular, deserves better.

Nahm, The Halkin, Halkin Street, London SW1 (Tel +44 020 7333 1234)
Lunch Monday-Friday £25, dinner Monday-Saturday £47 for the set menu

Mju, Millennium Hotel, Sloane Street, London SW3 (Tel +44 020 7201 6330)
Lunch £25, dinner £50 Monday-Friday