Sir Keir Starmer has told MPs suspected arson attacks on properties linked to him are “an attack on all of us, on democracy and the values that we stand for”.
Conservative leader Kemi Badenoch condemned the attacks as “completely unacceptable” at the beginning of their weekly Prime Minister’s Questions clash.
Police are continuing their investigation into the fires at north London properties and a car linked to Sir Keir.
A 21-year-old man was arrested at an address in Sydenham, south-east London, in the early hours of Tuesday on suspicion of arson with intent to endanger life and remains in custody.
Counter-terrorism officers are working “at pace” to establish the cause of the fires and “any potential motivation”, Scotland Yard said.
At Prime Minister’s Questions, Badenoch told the PM: “I think I speak for the whole house when I say that this wasn’t just an attack on him, but on all of us and on our democracy.”
Sir Keir thanked the opposition leader for contacting him “pretty well straight away” to lend her support.
In his first comments since the attacks, the prime minister said: “I really do appreciate that, and she’s absolutely right that this is an attack on all of us, on democracy and the values that we stand for.”
Liberal Democrat leader Sir Ed Davey said: “Can I offer our support to the prime minister and his family after the appalling arson attacks on his home.
“And can I echo his thanks to our brilliant police and firefighters.”
Emergency services responded to a fire at the prime minister’s private home in Kentish Town, north London, early on Monday.
On Sunday, crews were called to a small fire at the front door of a house converted into flats in nearby Islington – a property Sir Keir is understood to have lived in during the 1990s.
Police are also looking at a car fire which took place on Thursday on the same street as the Kentish Town property. It is understood that the car used to belong to Sir Keir.
The prime minister is understood to still own the home in Kentish Town but lives in Downing Street. He lived there before the 2024 general election and it has been rented out since then.
Counter-terrorism police are leading the inquiry and are treating the fires as suspicious.
Commander Dominic Murphy, head of the Metropolitan Police’s counter-terrorism command, acknowledged the probe may cause concern to MPs.
He encouraged any of them worried about their safety to get in touch with Operation Bridger, the specialist unit set up to protect MPs.