Dog owners have been urged not to leave their pets in hot cars after supermarket staff were forced to put out a tannoy message to rescue a hound trapped in a vehicle.

Staff at Leiston's East of England Co-op put out the message on Sunday, when temperatures peaked at about 30C.

It is believed the car's windows were slightly open at the time and that the car left quickly after the announcement was made.

Tests show that temperatures inside cars can increase quickly when they are left parked in the sun.

Essex Police's Dog Unit tweeted over the weekend that it had seen a 13C increase in the temperature of its car while left in the sun - which had no dogs in it at the time - in just the space of 30 minutes.

Katie Chamberlain, from Leiston, was in the shop at the time.

"It's a sweatbox," said Miss Chamberlain.

"In my opinion, it's complete and utter abuse."

A number of UK charities, including the RSPCA, are part of the The Dogs Die in Hot Cars coalition group.

It launched a campaign earlier this year to protect pets from suffering during the hot weather, which is called ‘Stay home, Protect dogs, Save lives’.

RSPCA dog welfare expert Dr Samantha Gaines said: “We know families love their pets and want to keep them close but, sometimes, it may be safer to leave your four-legged friends at home.

"Dogs can suffer from heatstroke during hot weather and this can be extremely dangerous, and even prove fatal.

“We’re calling on pet owners to put the welfare of their dogs first this summer.

"If you’re heading out and about then consider whether your pet may be happier in the cool at home, only walk them during the cooler hours of the day, and never leave your dog in a car unattended on a warm day.”

Official advice states that if you see an animal is displaying any sign of heatstroke such as panting heavily, drooling excessively, is lethargic, collapsed or vomiting, you should dial dial 999 and report a dog in a hot car to police.

In extreme circumstances, you can break the window - but you must have proper justification or this could be deemed criminal damage.