More than 550 MPs and peers have urged Sir Keir Starmer to proscribe Iran's Islamic Revolutionary Guard Corps (IRGC) as a terrorist organisation.
The cross-party call comes as three Iranians appeared in court accused of spying on Tehran dissidents now living in Britain.
Lawmakers described the Iranian regime as "faltering" and warned that any policy of appeasement would betray democratic values and undermine global security.
The court heard that Mostafa Sepahvand, 39, Farhad Javadi Manesh, 44, and Shapoor Qalehali Khani Noori, 56, appeared at Westminster Magistrates' Court accused of allegedly staking out homes linked to media outlet Iran International, which is renowned for being critical of the current regime in Iran.
Starmer has been pushed to designate the Iranian Islamic Revolutionary Guard Corps a terrorist organisation
PAThe men were also charged with engaging in conduct likely to assist a foreign intelligence service.
According to court proceedings, the men had arrived in Britain on small boats and by lorry, and were granted temporary leave to remain after claiming asylum.
The cross-party statement emphasised that the Iranian regime completely blocked all routes for political activity.
It called on the international community to recognise the Iranian people's right to seek a regime change.
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Lawmakers noted that more than 1,000 executions have taken place in Iran in 2025, with Amnesty International reporting that 64 per cent of all documented executions worldwide in 2024 occurred in Iran.
They also warned about the regime's so-called "Hijab and Chastity Law", which enforces mandatory hijab-wearing and suppresses women.
Tory MP Bob Blackman, Chairman of the 1922 Committee, who sponsored the initiative, said: "It is time to change course on Iran policy.
"We should align our policy with the major shifts that have occurred in Iran and the region. We must stand with the Iranian people and the organised resistance, led by Maryam Rajavi and her 10-point plan."
Tory MP Bob Blackman has called for a change of policy for Iran
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The Tory MP explained that "Iranian terrorism has reached our soil" and "a serious terror plot, involving several Iranians, was recently thwarted in the UK".
Blackman encouraged the UK to follow suit with the US, which designated the IRGC as a terrorist entity several years ago.
Ex-Minister David Jones added: "The extent of support for this cross-party initiative shows a growing consensus among UK politicians that the time for a new policy on Iran has arrived.
"No more procrastination - it only aggravates the problem."
