It’s been four years since a British prime minister stepped into the White House and during that time the leading characters and the context in which they are meeting have changed greatly.

President Donald Trump and Theresa May replaced by President Joe Biden and Boris Johnson. Brexit has happened; the ‘forever war’ in Afghanistan is over; and the two incumbents in the White House and Downing Street have found common purpose on climate change.

Hence the gift to President Biden from Boris Johnson, a signed copy of Tim Peake’s Hello, Is This Planet Earth?. In it an inscription: “I hope this book provides a reminder of what we’re fighting to save as our countries tackle climate change together.”

And for President Biden’s part, he presented Mr Johnson with a framed picture of the pair at Cornwall’s Carbis Bay, where he first spent time with his UK counterpart at the G7 and which he told the prime minister he really liked in their 90 minute bilateral meeting on Tuesday.

From No 10’s perspective, I’m told the last seven days have delivered more than the they hoped for: The UK has participated in a major security partnership with the US and Australia to develop nuclear power submarines, which one insider described to me as “a major milestone’ in the strategic shift to the Indo-pacific as outlined in Mr Johnson’s major integrated review of the UK’s security, defence, development and foreign policy.

The PM has also finally secured a deal to allow double-jabbed Britons to travel to the US and seen President Biden commit billions more annually to the $100bn climate aid fund ahead of COP26. “It gives us huge momentum into the next six weeks, not just the specific commitments from the US, but the way in which this will galvanise other countries, we are working on a shared agenda.”

But for all the accord, there is a big glaring gap in one key area – the signing of a free trade deal which Boris Johnson has championed as a big Brexit bonus. President Trump had said Britain was “at the front of the queue” in 2017 but now it seems that the US has signalled to the UK not to even bother to wait in line.

When I pressed the prime minister on getting that post-Brexit deal done by 2024 – a full four years after Brexit – he refused to commit and now one senior source suggests the UK has all but given up on landing its own free trade agreement, considering instead whether to leapfrog into the trade deal between the US, Canada and Mexico or perhaps cut a series of smaller deals instead.

The prime minister has framed it as the US president having “other fish to fry” as he pushes through his big post-COVID infrastructure package through Congress. The PM stressed to me in our interview in New York that he wanted the right deal not a rushed deal.

But, there is a point of tension to all of this, a note of visceral discord and it centres around thee post-Brexit arrangements for Northern Ireland.

When I asked this Irish-American president in the Oval Office whether concerns over Northern Ireland Protocol – designed to protect the peace process Northern Ireland – was holding back a trade deal, the warning to the man sitting by his side was clear; don’t allow tensions over post-Brexit trade rules to destabilise the Irish peace process – something President Biden feels “very strongly” about. “I would not all like to see, nor would many of my Republican colleagues like to see a change in the Irish Accords, the end result having a closed border again.”

Brexit and the fall-out for Northern Ireland will be high on the agenda on Wednesday when the prime minister meets with Democrats on Capitol Hill. For all the common ground between President Biden and Boris Johnson, Brexit and Northern Ireland are the flies in the ointment and until they’re resolved its hard to see whether that trade deal will be taken back off the shelf.