Martin Clunes has written to Scotland Yard urging officers do more to catch the so-called Cat Ripper of Croydon. The TV star said at least 35 cats are thought to have been mutilated in the south London borough, calling it the "stuff of nightmares".

The 54-year-old actor, who went to school in Croydon, wrote a letter to the Metropolitan police commissioner, Sir Bernard Hogan-Howe, on behalf of animal rights group Peta. He warned the "sick" killer could start attacking humans next.

He wrote: "As someone who shares my home with several four-legged companions, I read with horror that some of the cats had been decapitated, disembowelled or dismembered – this is the stuff of nightmares. The local community is understandably distraught and frightened. No one feels safe while this sick individual is on the loose."

Clunes went on to say that many animal abusers also commit serious violent crimes against humans, adding: "Research in psychology and criminology shows that people who commit acts of cruelty to animals don't stop there – many of them move on to their fellow humans. That is a scary thought indeed."

A host of celebrities have already voiced their concern about the risk the killer poses to animals, including X Factor presenters Caroline Flack and Dermot O'Leary. Reports police were investigating the killings first emerged in December, with the cats believed to have been attacked with some sort of blade.

One feline was discovered in a hedge near her owners' home in Coulsdon with her head and tail removed and her body so badly mutilated that she had to be identified by microchip.

Dr Adam Lynes, a lecturer in criminology at Birmingham City University, had told the Sun: "To me, this looks like the work of a single disturbed individual. The fact that several bodies were found with heads and tails removed suggests that it's the same person behind the attacks.

"The person responsible is likely to be enjoying having the power of life and death over a defenceless animal. But the fact they took trophies to remember the attacks suggests the killer is enjoying the cruelty and pain caused during the deaths, which were extremely brutal."

He added: "Unless the person responsible is caught soon, I think it's very likely they will continue to kill more cats — and they could even make the leap to attacking humans."

Peta is offering a £5,000 reward for information leading to a conviction. The group said in a statement: "We're also asking people who live in the Croydon or West Norwood area to keep their cats safely indoors – and to keep an eye out for any suspicious activity."

The Metropolitan Police confirmed in December it had received reports of animals being harmed and was working with Surrey Police to investigate. Surrey Police's Sergeant Ross Spanton said at the time: "I would like to reassure the local community that active enquiries are under way to identify those responsible, and I would urge anyone with any information to contact the police."