A third man has been arrested in connection with fires at two properties and a car linked to Prime Minister Sir Keir Starmer.
The Metropolitan Police said a 34-year-old was arrested this morning in the Chelsea area of west London on suspicion of conspiracy to commit arson with intent to endanger life.
On Saturday, a 26-year-old man was arrested at Luton Airport on suspicion of the same offence.
He is currently still in police custody after a warrant of further detention was obtained at Westminster Magistrates' Court.
It comes after a Ukrainian man, 21, was charged with three counts of arson with intent to endanger life.
Roman Lavrynovych appeared at Westminster Magistrates' Court on Friday and was remanded in custody.
Lavrynovych, of Sydenham, south-east London, denied arson in a police interview.
He is due to appear at the Old Bailey in London in June.
The arrests come after a fire in the early hours of 12 May at a house in Kentish Town, north London, where Sir Keir lived with his family before the election.
Damage was caused to the property's entrance, but nobody was hurt.
A car was also set alight in the same street on 8 May.
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There was another blaze at the front door of a house converted into flats in Islington, also linked to the prime minister, on 11 May.
One person was taken to safety via an internal staircase by crews wearing breathing apparatus.
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