The birds have flown inside netting put up inside the submarine HMS Alliance at the Royal Navy Submarine Museum in Gosport.

The situation has caused concern among animal rights activists who are worried the birds will hurt themselves as they try to escape the netting.

Nicci Tapping, member of the Southern Animal Rights Coalition, said: 'We've heard reports the pigeons are frantically bashing themselves against the nylon netting in an attempt to escape.

'People don't seem to care much about pigeons, but they are living animals and need to be treated with respect.'

But museum managers say they are feeding and watering the trapped birds, even though they are a health hazard and need to be removed.

They say there are some holes the birds can escape through and all will be driven out over the coming weeks.

Bob Mealings, curator and deputy director, said: 'The museum is renewing netting and meshing on board HMS Alliance in order to provide a permanent means of stopping pigeons roosting inside the free flood areas of the vessel.

'However, certain points of access are being left open while the most difficult parts of the vessel are being netted.'

Mr Mealings said that over the next 10 days all but one or two holes would be blocked.

Then members of staff would shoo the remaining birds out through those holes.

He said: 'None of the birds are being harmed. Our strategy has been approved by the RSPCA.'

The pigeons are trapped in the flooding casing of the submarine.