A tiger with a chest infection, a caesarean section for a cow or a cat run over by a car... Just who does a zoo keeper, farmer or pet owner turn to in an animal's hour of need? Increasingly, it seems, to a doctor.

Generations of television and radio favourites such as Emergency Ward 10, All Creatures Great and Small and The Archers might have helped to educate the public on the difference between their local GP and a vet, but doctors are increasingly being asked to operate more like James Herriott than Dr Kildare.

Doctors' legal advisers are uncertain whether this is a vote of confidence in the NHS or a protest against excessive veterinary bills. Either way, the Medical Defence Union said it could not help if any treatment went wrong and a claim was made against a doctor-turned-vet. Wider NHS indemnity only caters for human patients, too.

Emma Sedgwick, MDU's medical-legal adviser, said increasing numbers of doctors were inquiring about their legal and ethical position.

"They ask if it is OK to help the neighbour's cat that's been knocked down by a car or to assist a local farmer with a lambing emergency. Some members have even been asked to pop down to their local zoo to use their specialist skills on more exotic creatures.

"We don't know why more doctors are seeking our advice on this topic. Perhaps with the rising cost of vets' bills, they are tempted to help out with a bit of DIY veterinary practice."

The Veterinary Surgeons Act 1966 is actually stricter about who can treat animals than rules and guidelines covering doctors and human patients. Only qualified and registered vets can carry out veterinary surgery, unless they specifically ask doctors, for instance.

"This has been arranged for exotic creatures at the zoo, but is extremely unlikely in the case of the bunny next door", said Dr Sedgwick.

"With specialist doctors, it is often the case that no one else has their skills, so they are the only ones who can perform the operations, even if they have only ever seen a tiger on TV before."

A spokeswoman for the British Veterinary Association pointed out that animals could not give their permission to have someone other than a vet treating them, whereas vets could treat humans, if the patients agreed.

As to the difference in the bills, she said: "We have often said pets should be on the national health.

"There are benefits animals can bring (to human patients), to recovery after strokes, for instance. There may be a feeling of 'I am going to the doctor, let's see if I can get the pet treated as well'."