More than 90 per cent of London diners welcome the smoking ban, with a third saying they have started eating out more since its introduction.

In the first major survey since the new rules came into force on 1 July, 93 per cent of more than 5,000 diners questioned said they were in favour of the ban. The news comes in the same week that researchers in Scotland found that heart attack rates have dropped 17 per cent and air quality in restaurants and pubs has dramatically improved since smoking in public was banned there.

Martin Couchman, deputy chief executive of the British Hospitality Association, said: "Many restaurants turned non-smoking without legislationbut it has helped those who weren't quite sure what the impact would be to become fresher places and given them the extra push.

"The findings don't particularly surprise me. I think restaurateurs would prefer diners to enjoy the food rather than the smoke."

Today's survey, carried out by restaurant guide Zagat, also found that London diners are still concerned about poor service, with 53 per cent of respondents citing it as their main gripe about eating out.

The researchers found that London officially has the most expensive restaurants in the world. Over the past year the average price of a meal has risen to £39.

The key dining trends this year include a greater emphasis on organic food and renewed enthusiasm for European cuisine and "haute couture" restaurants.

More than half of the diners questioned said they would be willing to pay more for organic food but some chefs have already responded - Tom's Kitchen in Cale Street, South Kensington, the latest venture from chef Tom Aikens, features photographs of suppliers on the walls.

The survey found tastes have become more European. Although Asian food is still popular, Italian food was the favourite with a quarter of those questioned.

The guide says the most upandcoming location to eat out this year is likely to be Mayfair, with a string of new restaurants.

Dining at more expensive restaurants is growing in popularity, with over a third of respondents preferring the more formal to the casual option. Chez Bruce in Wandsworth claimed the top food honour, ending Gordon Ramsay's Chelsea restaurant's sevenyear winning streak. Tim Zagat, cofounder of Zagat, said today: "It's astonishing to see how expensive the London dining scene has become. It's interesting to note that the average cost of a meal at the top-rated Chez Bruce (£57) is a full £50 less than the runner-up, Gordon Ramsay (£107)."

• Zagat London Restaurants 2008 is published today, price £9.99.