That old chestnut - a deal that seems too good to be true usually is - holds true for some package holiday deals. A recent survey involving travel agents' advertisements was conducted with interesting results by the UK Consumers' Association and magazine Which?

The organisation made anonymous visits to travel agents in 10 locations in the UK to ask about the late deals and special offers advertised in the windows. Many of the ads trumpeted "late deals", "special offers", "manager's specials" and "today's megadeals".

Of those companies surveyed - Co-op Travelcare, Going Places, independent agents, Lunn Poly and Thomas Cook - 40 per cent of holidays asked for by the survey team had already been sold. When asked why the holidays were unavailable the researchers were told they sold so quickly they didn't have time to remove the cards. Which? found that the frequency of updating window advertisements ranged from every half hour to once a week depending on the travel agency.

Overall, only one-third of the 94 holidays asked about were available at the price advertised in the window. "Of the 55 holidays that were still available, 24 turned out to be more expensive than the advertised price. Half of these were between £40 sterling (€65) and £73 sterling more expensive and almost a quarter between £99 sterling and £200 sterling more expensive," says Which?

The majority of agents explained away the price differences by saying the tour operator had recently increased the price, says the magazine. At the company with one of the worst survey ratings, Going Places, "Most of its agents told us that the prices change all the time and it was impossible to keep up. Several said that if the holidays proved to be popular, the tour operator would put the price up."

One of the company's holidays to Gran Canaria, which was advertised at £319 sterling really cost £489 sterling for a survey member. Another to the Algarve increased from £282 sterling to £482 sterling because it now included a named bed and breakfast rather than self-catering accommodation. In other cases, advertised rates were for several people sharing or did not include supplement costs although this was not specified in the window advertisements.

Which? says trading standard officers in the UK have suggested that unavailable low-cost holidays were sometimes left in the window to entice customers to come inside and then offer them a more expensive holiday. The magazine found that the majority of alternatives suggested by travel agents were more expensive.

Some travel agents and package holiday providers here advertise special deals in their windows. Under European Union legislation, however, consumers are entitled to truth in advertising. The European consumer guide to the single market says the onus is on the advertiser to prove that their claims, such as prices, are true. If a travel agent or package holiday provider is consistently advertising holidays that are not available for the terms specified, consumers are advised to contact their relevant regulator or consumer body. In this case they are: the office of the Director of Consumer Affairs, the Consumers' Association of Ireland or the European Consumer Centre.