An industry largely built on the premise of 'beating the tax man' with heavily discounted purchases of alcohol and tobacco has become more diversified and sophisticated in the past decade. And sometimes this is reflected in the price.

'Increasingly, it focuses on exclusive items that cannot be found in any local market and a much wider range of fashion, accessories and gifts. If the shopper is really looking for bucket-shop prices, duty free is probably not the place to go. If you are looking for international brands - and you want to be sure that what you are buying is the genuine article - at a fair price, then it's a good bet.'

Recognising the trend, a number of the biggest fragrance and cosmetics launches are now conducted through duty free. In a marketing coup, Hong Kong International Airport recently attracted a number of international luxury brands to open their first airport shops in the world. Brands include Prada, Tiffany, Baccarat, Christian Dior and Ralph Lauren.

While discounts can still be found in duty free, it is very much a case of 'buyer beware'.

'Savings vary heavily, both by market and nationality,' he says. 'If you are a Chinese or an Indian citizen, you will make hefty savings on, say, a bottle of Johnnie Walker Black Label in duty free. If you come from a low-tax country, you won't. But generally, especially in Asia, alcohol and tobacco are good value and are guaranteed to be authentic merchandise.

'Fashion and gifts can vary wildly. In a shoppers' paradise like Hong Kong, travellers will always be able to pick up cheaper deals locally on many items. But the airport has the advantage of convenience, product guarantees and a wide selection of international brands.'

While leading international brands feature in most of the top airports, regional trends often mean the merchandise varies from country to country. Asia was historically skewed towards Cognac, and is now more inclined to high-priced blended Scotch whiskey. Europe is more of a malt-drinker's arena. Retailers tend to look at their customer profile by nationality and stock accordingly.

'Destination merchandise' is the new term for souvenirs - and is always a big seller at airports - but it doesn't mean the cuddly koala you have chosen as a holiday memento was actually made in Australia.

'Whenever I go through Hong Kong airport, I buy in the small but perfectly set-up Shanghai Tang store, because at least I can pick up a gift there with Asian character.

'If I'm travelling through London Heathrow airport, I'll head to the marvellous World of Whiskies store, which features an incredible range of great malts. That's what I call destination merchandise.'

The top five airport duty-free stores in the world are, in terms of turnover, London, Singapore, Amsterdam, Paris and Dubai.

Mr Moodie lists the best features of each:

Heathrow Airport, Britain: Duty-free shopping is best in Terminal Three, the long-haul terminal for most Asian traffic. This new development has a great range of traditional duty-free items (wines and spirits, perfume and cosmetics), and a mix of luxury and trendy brands, including Paul Smith, Rigby & Peller and (Moodie's favourite) Berry Bros wine store ('where you can find vintage Armagnac from every year dating back to the last century').

Changi Airport, Singapore: Clean and bright layout, with a strong emphasis on price. The Singapore airport authority insists that its retailers have better prices than other airports in Asia-Pacific. 'I love the Swizzle confectionery shop for its explosion of colours and fun - a great place to take the kids,' Mr Moodie says.

Charles de Gaulle Airport, France: Improving fast, but it needed to. The retailing here has changed hands too often in an airport where shoppers' needs were clearly an afterthought to the original architects. A newly commercial-minded airport authority is working hard to improve the retail offer. As you would expect, there is a very good range of French wines.

Dubai International Airport, UAE: The most high-profile duty-free store on the planet - and definitely one of the best. You can win a million dollars in a raffle or enter the draw for a Ferrari 456 GTA for just US$139. The whole airport is one giant duty-free store with a huge gold palm tree in the middle of the departures zone. Excellent pricing, and you can buy everything from Nido milk powder to a Rolex watch. Almost a holiday attraction in its own right.

* Martin Moodie has been commenting on the duty free and travel retail business for 16 years. Next year he launches The Moodie Report Travel Retail Awards, to recognise the best duty free shops in every category, in every region of the world.