Record numbers of dogs are being poisoned after being fed chocolate, grapes and raisins by their owners as treats, say vets.

Vets have seen a surge of almost 50 per cent in the number of dogs falling ill after eating chocolate.

In 2006, vets made 790 emergency calls about chocolate poisoning to the Veterinary Poisons Information Service. Last year, the figure was 1,166.

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The number of pets poisoned by eating grapes, raisins or sultanas has almost doubled from 117 in 2006 to 224 last year.

According to the service, which advises vets, a total of 17,000 cases of poisoned cats and dogs were reported last year - up 20 per cent on 2007.

Chocolate contains theobromine, a naturally occurring stimulant found in the cocoa bean, which affects the central nervous system and heart and can kill a dog.

The danger depends on the dog's size and the type of chocolate. Darker and more expensive chocolate contains more theobromine. Humans, and cats, have the metabolism to cope with theobromine.

Toxins in grapes, raisins or sultanas can cause renal failure in dogs. In some cases, small dogs have died after eating as few as four grapes. Vets believe many owners are unaware of the dangers and have fed their pets cake and biscuits containing chocolate or grapes as treats. In other cases the animals have helped themselves.

The figures do not show how many of the poisoned pets died.

Alexander Campbell, of the Veterinary Poisons Information Service, said: 'It often tends to be scavenging-type dogs, like labradors and Jack Russells, that find chocolate about the house and are attracted to the smell.'

There has also been a rise in the number of dogs eating painkillers. The number of dogs snapping up ibuprofen has gone up by 22 per cent, paracetamol by 20 per cent and aspirin by 24 per cent. These can sometimes be fatal.

Vets believe the animals sometimes find the drugs lying around the house. in many cases, however, pets are given the pills by their owners when they are injured, as it is cheaper than going to a vet.

There was a similar increase in the number of dogs treated after eating oral contraceptive tablets – the sixth most common cause of canine poisoning.

Most of the cases reported to the VPIS related to dogs, with cats second.

The most common cases of poisoning among cats involve animals that are treated using a type of flea treatment meant for dogs.

The service, which is part of a toxicology unit at London's Guy's and St Thomas' Hospital, also reported an increase in poisoned rabbits because of the growing trend for owners to keep the pets indoors.

Chris Laurence, veterinary director of the Dogs Trust, said: 'Dogs' habits don't change much and nor do people's. Dogs eat what they can and people will still eat chocolate, grapes and raisins and will still leave them around, while some will still feed them to their dogs.

'I wonder if people are a little bit more careless these days about leaving things lying around and with costs going up, are willing to try to give their pets their own pills.'