Nottinghamshire police force is being investigated by the RSPCA after two alsatian police dogs died when they were left in a car by their handler during the heatwave.

The force, which reported the animals' death to the organisation, had recently spent £300,000 on new kennels, it was revealed today.

The dogs were found dead in a private car which had been left in the car park at Nottinghamshire police headquarters in Arnold on Tuesday afternoon. Their handler, who was on duty, had gone inside some time before the dogs were found dead. The handler, who has not been suspended and is now at home on leave, could be prosecuted, the force confirmed. The maximum sentence for causing unnecessary suffering to an animal is six months in prison and a £20,000 fine.

The car park is close to the force's new kennels. The force has its own dog breeding programme but it is thought the alsatians had been donated by a breeder for public service.

Councillor John Clarke, the chairman of the Nottinghamshire Police Authority, said: "I think there will be some retribution for this at some point in the future. But I know the team will be mortified. It's a very close-knit team. It's tragic when you consider we have spent hundreds of thousands of pounds on kennels. Unfortunately tragedies do happen."

Peter Davies, the assistant chief constable, said: "This is a tragic incident and we value the important work our police dogs carry out on a daily basis. That is why we swiftly reported this incident to the RSPCA and we will be working with them very closely."

A spokesman for the Royal Society for the Prevention of Cruelty to Animals said: "It was reported to us yesterday by Nottinghamshire police. We are investigating and they are co-operating with us. I am sure this isn't the first incident and it won't be the last."

Police – who laid a bunch of white lilies, chrysanthemums and gypsophila outside their headquarters today – confirmed they had received complaints from angry members of the public.

The Independent Police Complaints Commission said it had received a referral from the force and was deciding whether to investigate.

The Dogs Trust, the UK's largest dog welfare charity, said it was "saddened" by the news. A spokeswoman said: "Whilst the cause of death is still to be determined, the charity would like to remind dog owners and police dog handlers that leaving your dog locked in a car can prove fatal, particularly during a heatwave. It can take just 20 minutes for a dog to die and temperatures reach over 40 degrees in some vehicles."