The luxury hotel market is not an easy market to define, and therefore even harder to value.
Consultancy PKF, for instance, classifies luxury hotels as being within its "superior deluxe" category, or anything with a room rate above £250.
Others put the cut-off at anything below five-star, although the development of the "four-star plus" sector is blurring even this definition at the edges.
Rod Taylor, hotels team leader at Barclays, argues that, if you are talking true luxury hotels, it is in fact a very small, select group of hotels, almost solely in London.
These, he argues, include prestigious names such as Claridge's, the Savoy, the Lanesborough and The Connaught as well as at the more boutique end, some hotels run by operators such as Firmdale or Orient Express.
Similarly, Philip Camble, senior manager within the travel, leisure and tourism advisory group at KPMG, points out that he knows of country house hotels, technically three star, that offer the sort of personal experience that should arguably put them in the luxury bracket when compared against chain four-star plus or five-star hotels, however well appointed.
What defines the sector is "the experience of the hotel package," stresses Camble.
After 9/11, the sector, which is still predominantly London centred, was devastated along with the rest of the capital's hotels.
Since then, again following the wider trend, things have picked up considerably. In March 2005 VisitLondon predicted luxury hotels would be one of the fastest growing sectors in the capital in the next five years, with more than 4,000 rooms opening.
According to Robert Barnard, partner at PKF, "superior deluxe" hotels have been reporting revenue per available room (revPAR) growth of around 7% on the back of improving occupancy rates. This end of the market, he argues, is often the first to fall but the first to recover.
What's more, rate generally lags behind occupancy by around a year to 18 months in any recovery, argues Camble.
"It is only when you can start to fill beds that you can start to manage them," he says.
On the property side, the luxury hotel market is most definitely buoyant, says Robert Seabrook, executive vice-president at Jones Lang Lasalle Hotels.
"There is quite a lot of activity going on around the market. London is as busy as I have known it to be. There is a general perception that the market is good," he says.
Well-located properties with good brand names will always be able to attract a premium, he adds.
The return of the American leisure traveller, or lack of it, has been one of the key trends of the past four years, argue the analysts.
While the American business traveller has by and large returned, the "high-rolling" leisure traveller has not come back so quickly, suggests Taylor.
They have been replaced, although not totally, by big spenders from Russia, Europe and the Far East, particularly from China and Japan, he argues.
"Before 9/11 these hotels were very, very dependent on the American leisure business travellers. After 9/11, of necessity, they have had to broaden their client base," says Taylor.
Another trend is the much greater City and institutional investment in the market than, say, a decade ago, suggests KPMG's Camble.
Players such as Blackstone, Colony Capital and Alchemy Partners are all active, he adds.
A survey by PricewaterhouseCoopers (PWC) in December 2004 found the luxury hotel sector was attracting wide interest from investors. London, it suggested, was leading the European post-9/11 recovery, with some hotels reporting achieved room rates of £400.
The purchase by Irish investment firm Quinlan of Savoy Group, including the Berkeley, Claridge's and The Connaught, is another case in point.
In an increasingly global market, foreign operators, such as Shangri-La Hotels, which is opening a hotel at London Bridge Tower and Spanish chain Silken, which is opening one at Aldwych, have begun to make inroads into the UK luxury market.
When it comes to hotel brands, ever more sophisticated and demanding time poor/cash-rich customers are leading to a continually growing range of facilities, suggests PKF's Barnard.
Some recently identified by PWC in the US included in-room fireplaces, in-room massage, shoeshine machines, ice delivered to your room, a menu of 10 types of pillow and butlers.
While people may look for the consistency of quality that a chain hotel brings when they are on business, when they are choosing a holiday destination and using their own money, they want something a bit different, agrees Camble.
"They want to go for individual, characterful, experiential hotels," he says.
Barring unforeseen shocks, Jones Lang Lasalle Hotels' Seabrook, for one, does not see anything else on the horizon that might knock the market sideways.
But, adds KPMG's Camble, there may be demographic issues at work that the luxury market in particular will need to address.
"The US tourist leisure visitor is not coming back in the same volumes yet. It may be economic, it may be fear but there is also an issue that a lot of these people that used to come are now just too old and not wanting to travel and the ‘old countries' do not have the same lure for the next generation," he says..
Luxury hotels since 9/11 have had to work harder at marketing and differentiating themselves to an increasingly unforgiving customer base, and this is likely to continue.
A poll by Thistle's luxury brand, Guoman, for instance in March 2005, found that nearly half of customers staying in luxury hotels felt their experience had not been good value for money.
They wanted a greater emphasis put on style and contemporary design, an investment that can put pressure on margins and, by its very nature, needs to be an ongoing investment.
On the amenities front, one area growing in popularity, predicts Camble, is the addition of in-room spa facilities, such as steam rooms, saunas and even treatment areas, something that, again, could pose problems for UK hoteliers.
"I think that is just around the corner. But if that does become a popular trend where are the older properties going to find the space?" he questions.