For more than 30 years, Ralph Kirshbaum bought two airline tickets for his trips. The world-renowned American musician, who lives in England, bought one seat for himself, and the other for his strong, silent companion – a priceless 250-year-old Montagnana cello.

But British authorities say Mr. Kirshbaum must now sit alone. Since police broke up an alleged plot to blow up transatlantic flights last month, restrictions have been placed on travelers: Nothing larger than a laptop bag can be carried into airplane cabins. But cellists, violinists, and French horn players are loath to consign their instruments, often antiquities worth millions of dollars, to cavalier baggage handlers and the rough-and-tumble conditions of the aircraft hold.

As a result, hundreds of musicians in Britain are complaining that the measures designed to thwart terrorists are in fact punishing virtuosos with nothing more malicious in mind than a Saint-Saëns solo.

The performers, who shuttle around the world to concerts, rehearsals, and festivals with ancient instruments in tow, are warning that their performances – and even livelihoods – are in jeopardy because the new rules make international travel almost impossible.

"The kind of international movement that musicians have come to rely upon and audiences have come to expect will be altered dramatically," says Kirshbaum. "If these policies are kept in place for any significant length of time, artists will rethink how frequently, if at all, they are going to make trips to Britain. There is enough stress and pressure in preparing properly for concerts to then have to add hours of needless travel on top."

Checking their instruments, often priceless, into the cargo hold isn't an option for most top musicians.

"Something like one in eight instruments gets damaged – no matter how much they assure [that the instruments will] be taken care of, they are very likely to get smashed," says British cellist Steven Isserlis, who travels with a 276-year-old Stradivarius instrument. "It's irreplaceable," he adds. "It's my responsibility to pass it on to the next generation."

The rules have resulted in some distinctly odd itineraries, as musicians resort to road and rail to get from A to B. Mr. Isserlis, for example, has already endured a 10-hour journey by train to Germany for a rehearsal instead of a simple one-hour flight. Kirshbaum says a quick hop to a festival in Italy this week turned into a 24-hour ordeal on Europe's rail network.

Many are finding that the only way to travel with their instruments is to take the three-hour Eurostar train to Paris and fly on from there. "A lot of British musicians work abroad," says Keith Ames of Britain's Musicians Union, which has been arguing over the restrictions with transport officials and intends to lobby Parliament about them. "If they can't take an instrument with them, how are they supposed to play? You can't ask them to borrow: That's like saying to Tiger Woods, 'Can you just borrow a set of clubs when you get there?' "

Mr. Ames says that the situation has become so bad that some appearances abroad are already in jeopardy, threatening cancellations, lawsuits, and insurance rows.

Already, the New York-based Orchestra of St Luke's has cancelled a tour of Britain. And the issue burst into the open on Saturday night when the conductor Mark Elder used the high-profile Last Night of the Proms concert at the Royal Albert Hall to plead for an end to the "unfair" restrictions. "Otherwise," he added "it seems to me that next year we should all look forward to Concerto for Laptop and Orchestra."

British officials say there is little they can do for musicians given the tight restrictions in place. One government official noted that musicians are not the only professionals affected: photographers, camera crews, and even lab technicians are finding it hard to live with the new rules. The government says it is consulting with airlines and airports to see if the restrictions can be modified or relaxed in the near future.

Musicians are not arguing that art should take precedence over security. But they are insisting on a special dispensation for those traveling with instruments that they argue are scannable and contain no internal working parts. Laptops, by contrast, would be more easily adapted to a terrorist's needs, argues Ames. "The idea that some bloke with a cello is a terrorist is laughable. Any terrorist would be more subtle than that," he says.

Kirshbaum says that the restrictions are not so much about enhanced security as about ensuring that staff are not overwhelmed by passengers with awkward baggage. "I was told it was not specifically a security issue; it was an issue of the volume of work that was put on the people manning the machines in the central search area. They were trying to minimize that."

But the outcome, he says, has been an enormous imposition on "the largest body of cultural ambassadors representing Britain." "We are flying the flag for Britain and they are putting shackles on us."

He says it is unthinkable to expect top musicians to travel without their instruments and beg or borrow replacements at their destination. "Our instrument is our voice," he says. "We spend hours every day living with, relating to, getting to know our instrument so that when we go on stage we are in the best possible position to give the best possible performance."

Isserlis, who has planned trips to New York and Japan in the fall, says it is audiences and culture in general that will suffer. "[Instruments are] much less dangerous than laptops and duty-free bottles of highly flammable liquids [such as liquor and perfume], but because they [airport authorities] make money out of that they'll never crack down on it," he says. "It's a threat to our livelihood and a threat to culture."