Until recently they were allowed to carry small instruments as long as they were smaller than 126 centimetres (50 inches) in length.

This meant that such items as violins could be carried in overhead lockers as part of the hand baggage allowance.

However a change in policy has cut the maximum length to 56 centimetres (22 inches) which, the Incorporated Society of Musicians says, means that instruments are being consigned to the hold.

The Society, which represents 6,000 professional musicians, has appealed to BA to reverse its policy and follow the example of easyJet, which has made special arrangements for instruments.

"It is almost unbelievable that British Airways should discriminate against musicians like this." said Julian Lloyd Webber, a cellist.

"The airline needs to realise that it is a service industry - and that includes providing a service to musicians who are among their most regular customers."

Deborah Annetts, Chief Executive of the Incorporated Society for Musicians, described BA's decision as baffling.

"It is unreasonable to expect precious and valuable instruments to be placed in the hold of an aeroplane and it can be prohibitively expensive for musicians to purchase an extra seat for a small instrument such as violin."

The easyJet agreement has allowed instruments such as violins, violas, piccolos, flutes, clarinets, bugles and trumpets to be brought on board, subject to available space.

A spokesman for the Society said musicians needed special treatment from airlines.

"Instruments are especially fragile (and wooden in the case of violins). A good instrument is very fragile and may be damaged by pressure and temperature in the hold of an aircraft. This isn't true for, say, video equipment."

A British Airways spokesman defended the airline's approach, which has seen it fall into line with most other airlines. "We do allow customers to carry small musical instruments on board our aircraft, provided they are within the maximum dimensions permitted for hand baggage.

"Where possible, we will allow customers to carry slightly larger instruments on board.

"However, customers may not be able to carry instruments on board if the flight is particularly busy, if they already have two items of hand baggage or when travelling in large groups.

"We believe our baggage policy is extremely generous as our customers can check-in a 23kg bag and carry two items of hand baggage free of charge."