A Ukrainian national charged over a series of arson attacks on houses and a car linked to British Prime Minister Keir Starmer appeared in a London court on Wednesday, the third man held over the incidents.

Over five days earlier this month, police were called to fires at a house in north London owned by Starmer, another at a property nearby where he used to live, and to a blaze involving a car that also used to belong to the British leader.

Petro Pochynok, 34, was charged with conspiracy to commit arson with intent to endanger life, police said in a statement.

Two men, Ukrainian Roman Lavrynovych, 21, and Romanian national Stanislav Carpiuc, 26, who was born in Ukraine, have both been remanded in police custody after being charged over the last few days in connection with the fires.

Pochynok appeared at London's Westminster Magistrates' court where he spoke only to confirm his age and address. He was remanded in custody until the next hearing at London's Old Bailey court on June 6 when all three men are due to appear. Judge Daniel Sternberg said a not guilty plea had been indicated on court papers.

None of the suspects have been charged under terrorism laws or the new National Security Act which aims to target hostile state activity.

Starmer, who has lived at his official 10 Downing Street residence in central London since becoming prime minister last July, has called the incidents "an attack on all of us, on our democracy and the values we stand for."