Britain and Iran have summoned each other’s envoys after three Iranians were charged with spying in the UK.

Three Iranian men were arrested on 3 May and appeared in court in London on Saturday on charges of spying for the Islamic republic.

Iran’s IRNA news agency said the British charge d’affaire was asked on Sunday to give an explanation for what it said was “unjustified” and “politically motivated” arrests. The UK Foreign Office then responded on Monday by summoning Tehran’s ambassador to the UK.

Home Secretary Yvette Cooper said the UK would “not tolerate growing state-backed threats on UK soil”.

“I can confirm the Iranian ambassador has been summoned and [Foreign Secretary David Lammy] is raising with Iranian foreign minister in the strongest terms that the UK will not accept any Iranian state threat activity in the UK,” she said in Parliament on Monday.

She added that the government would draft new powers of proscription to cover state threats.

She said they would create a power “stronger than current National Security Act powers in allowing us to restrict the activity and operations of foreign state-backed organisations in the UK.”

The Foreign Office said the government “is clear that protecting national security remains our top priority and Iran must be held accountable for its actions”.

“The [ambassador] summons follows this weekend’s announcement which stated that three Iranian nationals had been charged with engaging in conduct likely to assist a foreign intelligence service,” it added.

The alleged spying took place from August 2024 to February 2025, according to the Metropolitan Police.

Police have identified the suspects as Mostafa Sepahvand, 39, Farhad Javadi Manesh, 44, and Shapoor Qalehali Khani Noori, 55, all living in London.

A fourth man had been arrested on 9 May as part of the investigation, but was released without charge, the Met said.

The three men who were charged had arrived in the UK between 2016 and 2022 were granted temporary leave to remain after claiming asylum.

It is alleged they carried out surveillance with a view to locating journalists associated with Iran International, which produces coverage that is critical of the current regime in Iran. It has been proscribed in Iran as a terrorist organisation.

Home Secretary Cooper said the charges against the Iranian nationals came alongside a “series of grave wider issues”, including “rising numbers of Iran-linked operations on UK soil” and a “nearly 50% in a year” increase in MI5 state threats investigations.

“The Iranian regime poses an unacceptable threat to our domestic security which cannot continue,” she said.

Five other Iranian men were also arrested on 5 May in London, Swindon, Stockport, Rochdale and Manchester as part of a separate counter-terrorism investigation.

Four of the men – who had been held on suspicion of preparation of a terrorist act – had been released from custody, although the investigation “remains active and is ongoing”, police said.

The fifth man was earlier bailed to an unspecified date in May.