Larry the Cat, Downing Street's official mouse catcher, is thought to be threatened by Sir Keir Starmer's family cat JoJo when he moves into No10, an expert has claimed.

Larry, who is now at the ripe old age of 17, has called the government address home for longer than any UK leader and has served each Prime Minister as Chief Mouser for years. Over his term in office, the much-loved feline has seen many leaders come and go, and in the process has had to share his space with pet dogs, most recently Rishi Sunak's Labrador retriever Nova.

An expert has now claimed, however, that the territorial puss may struggle sharing its space with Starmer and his family's pet cat JoJo. Nicky Trevorrow, from Cats Protection, told the Daily Mail: "It's natural for cats to feel threatened when a new cat comes along, as they'll be protective of their territory and all the perks that come with it – like food, shelter and warmth.

"That's why it's important to take it really slowly, keep them in separate areas and get them used to each other's scent before they actually see each other. When they're familiar with another cat's smell, it'll make the face-to-face introduction much easier."

Larry the Cat was born a stray in 2007 and rescued from Battersea Dogs & Cats Home in 2011. He has been a beloved tenant of Number 10 and holds the title of Chief Mouser to the Cabinet Office. During a 2016 Prime Minister's Questions, David Cameron explained that Larry is a civil servant and not the personal property of any one individual.

He actually has official duties as well, with the Downing Street website stating he "spends his days greeting guests to the house, inspecting security defences and testing antique furniture for napping quality". It reads: "His day-to-day responsibilities also include contemplating a solution to the mouse occupancy of the house. Larry says this is still 'in tactical planning stage'."

Larry has also met his fair share of world leaders, as during a visit from Donald Trump he decided to lounge out behind the former President's £1.2 million armoured Cadillac. In 2011, David Cameron revealed to the BBC that Larry actually liked Barack Obama, saying: "Funnily enough, he liked Barack Obama. Obama gave him a stroke and he was all right with Obama." Sir Keir Starmer is now the sixth leader Larry has seen in office as he welcomes his first Labour government since being hired as a civil servant.