The UK government has announced sweeping new national security measures that will make it a criminal offence to support Iran’s Islamic Revolutionary Guard Corps (IRGC), stopping short of formally banning the organisation as a terrorist group but introducing some of the toughest restrictions ever imposed on it.

Prime Minister Keir Starmer confirmed that the IRGC will be designated under new powers created through the National Security Act. The move gives police and security agencies broader powers to investigate and prosecute anyone accused of supporting the organisation or acting on its behalf in the UK.

The government also announced the designation of two other groups. They include the Islamic Movement of Companions of the Right, which ministers say is linked to attacks against Jewish and Israeli targets in Britain, and the Russian GRU Volunteer Corps, an organisation connected to Russian military intelligence.

Announcing the measures, Starmer said the UK had already taken action against Iranian and Russian networks operating against British interests but argued the new legislation would make it significantly easier to prosecute those carrying out hostile activity inside the country.

He warned that anyone working on behalf of organisations that threaten Britain’s national security would face the full force of the law.

Home Secretary Shabana Mahmood said both Iran and Russia had increasingly relied on proxy groups to carry out hostile operations overseas. She said the new designations would give authorities stronger powers to identify, investigate and imprison those working for them.

The decision marks a significant shift after years of debate over whether the IRGC should be formally proscribed as a terrorist organisation. Previous governments resisted taking that step because of concerns it could severely damage diplomatic relations with Tehran.

In 2023, ministers chose instead to expand sanctions against the IRGC while stopping short of proscription, amid warnings that such a move could lead Iran to expel the UK’s ambassador and cut off important diplomatic channels.

The government says the latest action has been driven by a series of alleged threats linked to Iran, including reported assassination plots targeting two journalists working for Iran International in the UK and cyber attacks against infrastructure in Britain, Australia and Canada.

Under the new rules, anyone found to be supporting, assisting or benefiting from one of the designated organisations could face criminal prosecution. Those carrying out espionage or sabotage on behalf of the groups could receive a maximum sentence of life imprisonment.

Ministers also formally blamed the Islamic Movement of Companions of the Right, also known as Harakat Ashab al Yamin al Islamia, for a string of attacks targeting Jewish and Israeli-linked sites across Britain.

The organisation has claimed responsibility for seven incidents, including an arson attack that destroyed four ambulances in Golders Green, north west London, in March.

Security Minister Angela Eagle said intelligence assessments concluded that members of the IRGC’s elite al Quds Force were almost certainly directing the group’s operations across Europe.

The government also justified the designation of the Russian GRU Volunteer Corps by pointing to what it described as a pattern of hostile activity linked to Russian military intelligence.

Officials cited the 2018 Salisbury nerve agent attack alongside more recent acts of sabotage allegedly carried out by volunteer groups originally recruited to fight in Ukraine.

Angela Eagle said the government believed there was sufficient evidence to conclude that all three organisations were involved in activities posing a threat to the UK and that the designations were necessary to protect Britain’s national security.