Three dogs were slowly cooked alive when their owner, 65, left them in a hot car.

A dog owner has admitted causing the death of three pets after leaving them in his car for around five hours on a warm day while he went to the gym.

Jonathan Theobald pleaded guilty to causing the Staffordshire bull terrier-type dogs unnecessary suffering after being charged under the Animal Welfare Act.

The 65-year-old left Daisy, Mitch and Rascal in the vehicle parked outside Vivacity Gym in Peterborough for around five hours on June 16, with temperatures peaking at around 19C (66F), the RSPCA said.

Two of the dogs had already died by the time he returned to his car and he tried to save the third, the animal charity said.

'The dogs had been in the car alone for a number of hours,' RSPCA inspector Justin Stubbs said.

'They [the dogs] would have overheated. They may of have fits, they may have slowly cooked essentially, they would have been terrified, trapped. [It was] probably more of a emotional thing rather than a physical for those dogs.'

Preliminary post-mortem examinations showed the dogs died of heat exposure, the charity said, as it warned owners that conditions do not need to be overly hot to be fatal for an animal.

Mr Stubbs said: 'The weather was warm and it was humid but it wasn't hot that day. Met Office records show it was between 16C and 19C for the period of time these dogs were left.

No-one leaves their dog to die in a car on purpose. But there is no good reason to even risk it by taking your dog in your car in warm weather and leaving it while you just pop into the shop or just pop into your doctor's appointment. 'Not long' is still too long.' 

On the day the dogs were locked inside the car, temperatures outside peaked at 19C in Peterborough, Cambridgeshire.

The inside of a vehicle can reach temperatures 20C higher - meaning the dogs would have died in unbearable temperatures of almost 40C after being left without any water or ventilation.