John Bolton, pictured yesterday, is currently visiting London

Theresa May refused to take part in a US operation to protect ships in the gulf, the US's national security adviser has said.

John Bolton is currently visiting London and said the UK's original preference was to take part in a European operation.

But new Prime Minister Mr Johnson has reversed the previous government's policy and has now signed up to the US mission, as reported by The Sun.

Mr Bolton said: 'We were pleased PM Johnson's government has agreed to participate in Operation Sentinel, which reflects a change from the prior Government.

'Britain's original preference was to participate in some kind of European operation in the Gulf.

'It might have had a couple of British ships in it. I'm still looking for what the European ships would do.

'We felt the proposal we were making was far more likely to be successful.'

Former Foreign Secretary Jeremy Hunt is thought to have advised against the US plan, thinking Washington's stance on Iran was too hardline.

In his visit the US national security adviser also said the UK will be 'first in line' for a trade deal with the US - which could pursue a 'sector-by-sector' deal with Britain.

Speaking following a meeting with Prime Minister Boris Johnson on a visit to London, Mr Bolton said the US could focus on certain sectors like manufacturing and car-making where the two countries may agree, and work out more complicated areas later.

Theresa May refused to take part in a US operation to protect ships in the gulf, the US's national security adviser has said

Type 23 Royal Navy frigate HMS Kent leaves Portsmouth yesterday, heading for patrols in the Gulf

Mr Bolton said US trade negotiators think this is acceptable under World Trade Organisation rules.

Mr Bolton also said issues like security in Iran, and fears over Huawei's involvement in the UK's 5G network could wait until after Brexit to be resolved.

Mr Bolton said: 'A prior American president said that if the United Kingdom left the European Union, it would go to the back of the queue on trade deals.

'To be clear, in the Trump administration, Britain's constantly at the front of the trade queue, or line as we say.'

Mr Bolton said the US had been 'ready to negotiate' with Theresa May's government, and said the US could do a trade deal with the UK 'in pieces' on a sector-by-sector basis.

He said: 'We want to move very quickly. We wish we could have moved further along in this with the prior government.'

He added: 'We were ready to negotiate. We are ready to negotiate now.'