A third man has been arrested over suspected arson attacks on properties and a car linked to prime minister Sir Keir Starmer.
The 34-year-old was held in Chelsea, south-west London, on suspicion of conspiracy to commit arson with intent to endanger life on Monday, the Metropolitan Police said.
His arrest follows that of a 26-year-old man, who was detained on suspicion of the same offence on Saturday at Luton Airport.
Roman Lavrynovych, a 21-year-old Ukrainian man, has already been charged with three counts of arson with intent to endanger life in connection with the fires.
He appeared in court on Friday and was remanded in custody until a further hearing at the Old Bailey scheduled for 6 June.

Police were called by the London Fire Brigade to reports of a fire at an address in Kentish Town at 1.35am last Monday.
Damage was caused to the entrance of the property, where Sir Keir lived with his family before they moved into 10 Downing Street, but no one was injured.
A car linked to Sir Keir was set alight in the early hours of Thursday 8 May in the same street.
In the early hours of Sunday 11 May, firefighters dealt with a small fire at the front door of a house converted into flats in nearby Islington, which is also linked to Sir Keir.
The incidents have been widely condemned by politicians across the divide, with shadow justice secretary Robert Jenrick saying it is “important that the prime minister and anyone in public life has their family, their homes, protected”.
Speaking to Sky News, shadow justice secretary Robert Jenrick said it is “important that the prime minister and anyone in public life has their family, their homes, protected”.
“We have robust disagreements in politics but I want to ensure anyone who chooses to go in to public life feels that they’ll be properly protected and that we have civility in our debate”, he added.
“It is absolutely wrong, disgraceful, for any individual to take the kind of action that we saw against the prime minister’s home.”
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