Officers broke into the car, which was parked on Brighton seafront on Sunday evening (13 June) - one of the hottest days of the year.
One of the officers starts to force his baton through a back window, before smashing it open to free the dog.
The car alarm goes off, with the owners then filmed rushing straight towards the car, complaining to the officers.
A woman says: "You broke my window out," as she stands with her family.
An officer responds: "It's a hot day. You shouldn't be leaving the dog in the car in this weather."
Beachgoers watched the scene unfold as temperatures surged yesterday across the country.
One local, who had filmed the incident, said the owners didn't seem to be aware the heat was so dangerous.
Speaking to The Sun, they said: "Where they had parked there is just no shade.
"It's directly on the seafront in 25°C weather outside - I've got no idea what it was inside the car."
The witness told the publication he had seen one of the dogs panting in the car, while it was in a 'solid black cage'.
The owners were not happy to find the officers had broken in.
The witness said: "At first it was 'what the f*** are you doing, why did you break my car window? I was only gone for 10 minutes'.
"The bloke obviously thought he was completely in the right. He didn't really seem to have much empathy."
The RSPCA advises that an outside temperature of 22°C can reach 47°C inside the car within an hour.
Police advise anyone who sees a dog in a hot vehicle to dial 999.
A police spokesperson told The Sun: "Sussex Police were called about two dogs left locked inside a car in the heat of the day yesterday on Madeira Drive, Brighton.
"Police officers attended and tried to get a contact number for the owners of the car but were unable.
"Officers had no choice but to smash the side window to gain access and a kind member of the public donated a bottle of water.
"The owners were given strong words of advice on returning to the car a short time later.
"The dogs, who were much improved after fresh air and water, were left with the owners. Dog owners should never leave a dog alone in a car on a warm day. If you see a dog in distress in a hot car, dial 999. "
Featured Image Credit: Whitty Photography
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