Britain’s counter-terrorism police have arrested eight men, seven of whom are Iranian nationals, in two separate investigations, London’s Metropolitan Police said on Sunday.

On Saturday, five men, four of whom are Iranian nationals between the ages of 29 and 40, were detained on suspicion of terrorism offences over a plot to target a specific premises. The nationality of the fifth man remains unknown.

The arrests were made in Swindon, west London, Stockport, Rochdale and Manchester, police said, adding that officers were in contact with the site of the suspected target to provide relevant support.

They did not provide further information on the site, citing operational reasons.

“We are exploring various lines of enquiry to establish any potential motivation as well as to identify whether there may be any further risk to the public linked to this matter,” said Commander Dominic Murphy, who heads London police's Counter Terrorism Command.

The Embassy of Iran in London did not immediately respond to a request for comment.

The arrests come at a time of intense scrutiny of Iran-backed activities in Britain, with the country's domestic spy chief Ken McCallum saying last year that since 2022, officers had responded to 20 Tehran-backed plots that potentially posed lethal threats to UK citizens and residents.

In 2023, an Austrian national was convicted of carrying out “hostile reconnaissance” against the London headquarters of Iran International, a broadcaster which is critical of Iran’s government.

The following year, a British journalist of Iranian origin who worked for Iran International was stabbed in London.

The government has also placed Iran on the highest tier of foreign influence register, requiring it to register everything it does to exert political influence in the UK.

In another counter-terrorism investigation, which police said was not connected to the first, three Iranian nationals aged between 39 and 55 were arrested in London.

They were detained for suspected involvement in foreign power threat activity under the National Security Act, legislation which came into force in 2023 to counter hostile states' actions in the UK.

Searches were ongoing at their addresses, police added.