Tory grandee and former deputy Prime Minister, Lord Heseltine has admitted to strangling his mother's dog, saying the incident took place after the canine bit him. Heseltine also came under fire last week after saying that in a nine month spate, over 400 grey squirrels had been culled in their gardens.

In an interview with Tatler magazine, the Tory peer said that his mother's pet Alsatian, Kim, started biting him when he went to stroke it. "If you have a dog that turns, you just cannot risk it. So I took Kim's collar – a short of choker chain – and pulled it tight."

Heseltine said that Kim "suddenly" went limp. "I was devoted to Kim, but he'd obviously had some sort of mental breakdown."

The Daily Mail reported that rumours of Heseltine killing the dog had originally surfaced around 1992 as he challenged Prime Minister Margaret Thatcher's leadership but that they had been called an "exaggeration".

The RSPCA released a statement saying that they can only investigate offences "within three years of that alleged offence being committed. Therefore, in this instance, we are not able to look any further into this matter."

"The RSPCA would never condone an owner killing their dog themselves in this way. If a dog needs to be put to sleep then a qualified vet is the right person to euthanise an animal humanely and painlessly, not the dog's owner.

"There is no rule that says a dog should automatically be put to sleep if it bites someone."

They also said that dogs can become aggressive in response to being in pain: "It is important to get your pet checked by a vet as the dog may have become aggressive due to being in pain. If a vet rules out any form of illness or injury that could be causing the issue, they can then refer you to a behaviour expert for further help."

Heseltine said on ITV's Good Morning Britain on 25 October: "We culled over 400 squirrel in 70 acres in nine months, in other words we had an infestation and the truth of the matter is that the RSPB is more preoccupied by people who live in the towns and have a Walt Disney view of the countryside." One response on Twitter read: "Heseltine saying he culled 400 squirrels to help the wildlife? No you didn't you done it to benefit yourself."