For those who no longer give a hoot about owning a Vietnamese pot-bellied pig, here is the latest pet fashion accessory - the humble barn owl.

Increasing numbers of barn owls are being bought as domestic pets from garden centres, pet shops and even through the small ads of free newspapers. While bird lovers have for several years kept barn owls in aviaries in their gardens, the RSPCA is worried that people buying the birds as "in pets" are keeping them indoors and treating them as oversized budgies.

Last week, 21-year-old Neil Buckley from Barnsley, South Yorkshire, was fined pounds 200 for causing a barn owl unnecessary suffering after it had been found in a cage in his bedsit. In court, RSPCA inspector Graeme Petty said: "It appears that barn owls are the latest pets craze."

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The Barnsley court was told that the owl, which has a wingspan of 3ft, was kept in a cage only 18ins wide. "The bird was squeezed into the cage. It had damaged its wing tips and had suffered drastic weight loss because it found the situation so stressful. I believe it would have been dead in another two or three days," Mr Petty said.

The court heard that Buckley had been negligent rather than vindictive towards the owl, called Barney, which is now recovering at an animal sanctuary. It will never be released into the wild because it is now dependent on humans and can not hunt.

Other RSPCA prosecutions include a man who kept a barn owl caged by wire in a kitchen cupboard and another who kept one in a parrot cage. "It is a cause for concern for us," said RSPCA spokeswoman Justine Pannett. "We've had reports of them being sold in all sorts of places."

Mr Petty said it was inappropriate to keep barn owls as pets. "It is not like keeping a budgie. Barn owls require a large aviary with a lot of open space. They are very shy and unsociable. They like to swoop on their prey rather than have it fed to them on a perch. The best place to see them is in the wild."

He believes unscrupulous breeders are taking advantage of the Wildlife and Countryside Act which allows barn owls (an endangered species) that have been ringed and bred in captivity to be sold as pets.

Barn owls are sold for around pounds 30. "Unfortunately, if there is a market for these birds then someone will step in to meet the demand," he said.