The UK and US will have an "unprecedented partnership" post-Brexit, Donald Trump's national security advisor has said, adding that Britain will be "first in line" for a trade deal.
After meeting Prime Minister Boris Johnson, John Bolton tweeted, saying the pair had discussed "trade, security, and opportunities to deepen our bilateral relationship after the UK leaves the EU.
"The US and UK are on course for an unprecedented partnership."
Mr Bolton also said that while a trade deal would be done first, other deals in areas such as financial services and agriculture could be agreed on a gradual "sector-by-sector" basis.
Mr Bolton said the US could focus on striking bilateral trade deals in certain sectors like manufacturing and car-making where the two countries may agree, and work out more complicated areas later.
Mr Johnson however admitted he expects negotiating a post-Brexit trade deal with the US to be a "tough old haggle", but said he's confident Britain "will get there".
"We have fantastic opportunities to open that up. Actually the US market is growing very fast for the UK, but they still ban haggis, for Heaven's sake.
"In the US there are all sorts of opportunities we have to open up trade, but that also goes for companies around the world, but the single biggest deal we need to do is a free trade deal agreement with our friends and partners over the Channel."
He added: "In my experience the Americans are very tough negotiators indeed, and we will do a great deal with them and it will open up opportunities for UK business, particularly service companies in the US, but it will be a tough old haggle - but we will get there."
This comes as pollsters say a majority of the British public think Mr Johnson should suspend Parliament in order to push through Brexit.
Mr Bolton said: “The main purpose of the visit really is to convey President Trump’s desire to see a successful exit from the European Union for the United Kingdom on October 31, to offer to be of help in any way that we can and to express his hope we can have a fully comprehensive bilateral trade agreement with the United Kingdom as soon as possible.”
He added: "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 could do a trade deal with the UK “in pieces” and concentrate on areas, like manufacturing and the car-making industry, they can agree on first.
He said: “You could do it sector by sector, you could do it in a modular fashion in other words.
"You could carve out some areas where it might be possible to reach a bilateral agreement very quickly, very straightforwardly.
“That would then lock that in and when the other areas that might be more difficult were concluded later, you could combine it in one overall agreement.
"So the objective is either one document or a series of agreements that would be comprehensive.
“In order to expedite things and enhance the possibility for increasing the trade and investments between the two countries, doing it in a sector-by-sector approach or some other approach that the trade negotiators might agree with, we are open to that.”
He added: “The idea of doing it in pieces rather than waiting for the whole thing is not unprecedented.
"I think here we see the importance and urgency of doing as much as we can agree on as rapidly as possible because of the impending October 31 exit date.”
Asked whether piecemeal trade agreements like this are allowed under WTO rules, Mr Bolton said: “Our trade negotiators seem to think it is.”