Britain's auction houses lose millions due to anti-terror laws restricting movement of art pieces

The strict measures have put a stop to secret international previews of priceless art which in the past netted Britain millions of pounds in international trade.

Until now, auction-house curators carried artefacts, including jewels and Old Master paintings, as hand-baggage to exclusive showings around the world.

The private viewings, sometimes in the homes of wealthy bidders, are used to persuade the very rich to bid on items in the London salerooms of top auction houses such as Christie's and Sotheby's.

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These wealthy collectors – who include oil barons, Arab princes, Russian billionaires and celebrities – often bid anonymously using agents or dedicated hotlines, and their involvement can help push prices to record levels.

In just one week in June last year, a series of sales in London raised a record £260million.

But the ban on extra in-flight baggage, brought in after MI5 foiled last year's alleged plot to bring down transatlantic flights, has prevented the practice and seen much of the business transferred abroad.

Despite behind-the-scenes lobbying by the auction houses, the Department for Transport restrictions have not been waived for the art trade.

In the past, art worth up to £50million has been carried on flights in this way.

Items are put in specially designed wheelie bags and, if small enough, stowed in overhead lockers.

Larger pieces require the auction houses to buy an extra seat next to the courier, while paintings, in protective carrying cases, are secured to a business-class seat, using seat-belt extensions designed for babies.

Before the auction of the late Princess Margaret's jewels last year – a sale that eventually raised more than £10million – several of the more valuable items were taken to previews abroad, visiting Switzerland, Hong Kong and New York.

Among the pieces was a Fabergé clock given to the Princess by her grandmother, Queen Mary.

The clock sold for £1.24million – double its expected price.

Also taken abroad was the Poltimore Tiara, created by jewellers Garrard in 1870, which Princess Margaret wore on her wedding day.

Airline passengers would have been unaware that a humble-looking wheelie bag carried by someone in business class contained the valuable collection.

The Department of Culture has said the UK art market is worth £3.4billion a year, making it the second largest in the world, behind the United States.

But there are fears that this position could be damaged by the decision not to allow auction houses to carry extra baggage.

An art industry source said last night: "The art trade provides Britain with prestige and millions of pounds of revenue every year.

"The Government's refusal to allow an exception to one-bag rules for these priceless items has badly damaged this trade.

"We all understand the threat we face from terrorism, but Britain has been damaged by the blinkered approach of the Government.

"Instead, items are being sold in New York or Paris, costing Britain millions of pounds in lost trade – something that, even when the ban is lifted, may be difficult to get back."

Yesterday, both Christie's and Sotheby's were reluctant to discuss the problems.

A Christie's spokesman said: "Works of art are sometimes taken and presented to our clients abroad.

"However, we do not discuss the movement of art for security reasons."

Last month, Gordon Brown announced that the one-bag restrictions would be eased from January.

The Department for Transport said the rule had been introduced to relieve the strain on security staff facing new and sophisticated terror threats.