The PM will chair a meeting of the Government's emergency Cobra committee today.

Monday 22 July - Downing Street said the Prime Minister would be updated by ministers and officials on the situation and 'discuss the maintenance of the security of shipping in the Persian Gulf'.

But senior Tory MPs are stepping up their criticism of Mrs May following claims the Government rejected the offer of US naval protection for UK tankers travelling in the Strait of Hormuz, the world's busiest shipping route.

Members of the Iranian Revolutionary Guard boarded the Stena Impero on Friday night, claiming it was a 'reciprocal action' following the British interception of an Iranian tanker near Gibraltar earlier this month. 

Speaking to the BBC's Westminster Hour, Tory MP Huw Merriman, parliamentary aide to Chancellor Philip Hammond, said: 'I take the view that we have dropped the ball here.'

We knew from 4 July, having seized an Iranian tanker that we suspected was breaching EU sanctions and heading for oil to Syria, that there would be some form of reprisal and that’s exactly what we’ve got.'

'The reality is you’ve got 12 escort vessels around the world that we have, in terms of capability and we did not put in place a chain where we asked all of our vessels to leave at a certain time under convoy, or work with the US to make sure that we had a wider coalition of convoy. So it was hardly a surprise when one of ours got taken.'

'I take the view that we have dropped the ball here.'

Iain Duncan Smith, who is heading up Boris Johnson's campaign to be Conservative leader, accused Mrs May of making a 'major miscalculation' by turning down an offer of US protection for British ships from President Donald Trump.

The former Tory leader said: 'Britain was offered whatever assistance is necessary to protect British ships and commanders out there were willing to help.'

'The Government failed to take them up on the offer and the reason was that we didn’t want to upset the Iranians.'

'They made a major miscalculation. It was a big misjudgement and it goes all the way to the top.'

Mr Hunt, the Foreign Secretary and Conservative leadership rival to Mr Johnson, has warned Iran of 'serious consequences' over the move.

But he has made clear that Britain is not contemplating military action in response at this time.

He said this weekend: 'Our priority continues to be to find a way to de-escalate the situation'.

The incident comes amid heightened tensions in the region following the United States' decision to withdraw from an international deal designed to curb Iran's nuclear program and reimpose economic sanctions on the country.

Iran has hit back by exceeding uranium enrichment limits set under the nuclear deal, a move branded 'destabilising' by the UK government.