Joe Biden will meet King Charles for the first time since the coronation, in a fleeting UK visit that will be used by Rishi Sunak and the US president as a “pre-meeting” ahead of joint efforts at this week’s Nato summit. However, what will be the sixth meeting between Biden and Sunak since Sunak took office in October has been partly overshadowed by the US president’s decision to send cluster munitions to Ukraine, weapons that are prohibited by 100 countries including the UK, which currently holds the presidency of a convention banning them. Sunak – who said in careful comments on Saturday that Britain “discouraged” the use of cluster munitions – has a choice about how much to make of the difference when Biden visits Downing Street on Monday morning, but it is likely to be limited as the prime minister seeks to continue the process of repairing UK-US ties frayed over the course of the Donald Trump, Boris Johnson and Liz Truss premierships. Biden said on Sunday that providing the weapons had been a very difficult decision for him and, without naming the UK, added he had discussed it with allies. They were being provided because Ukraine was running out of ammunition at time when its forces were engaged in their offensive and needed to get through Russian trenches, he told CNN. But Tobias Ellwood, a Tory MP and chair of the defence select committee, warned it could cost the “high moral ground” for Ukraine’s backers. “And that could easily see this international coalition of support for Ukraine start to crumble away, because many people will be deeply concerned that we’re using munitions which have been outlawed,” he told GB News. Biden will later meet the king in what will be seen as a move to dispel allegations on the right that the president had snubbed Britain by not attending the coronation. However brief – Airforce 1 is scheduled to have wheels up in time to arrive in Vilnius on Monday evening – the visit has pluses for Biden and Sunak, and comes at a particularly welcome time for the latter, as observers such as Sir Kim Darroch, British ambassador to the US from 2016 to 2019, have noted. “There is still a fascination on the part of the American public with the royals, so that image will be useful to Biden, but also the one area where the UK continues to have credibility with Washington is on defence and security, so he will be looking to ensure Sunak will be a supporter and enabler of him at the Nato summit,” he said. “For Sunak, who has had a nightmare few weeks and faces some difficult political tests in the form of several byelections, it will an opportunity for him to be seen as a world leader ahead of a summit where some quite big decisions are coming up, including on the issue of Ukraine’s application to join.” Meanwhile, polling shared with the Guardian by the British Foreign Policy Group, a UK thinktank, reflected the extent to which the turmoil of Brexit and the Trump presidency may have had an impact on British public attitudes to the US. Less than half (48%) of more than 2,000 people surveyed with JL Partners at the end of May and start of June trusted the US to act responsibly in the world. There was also a cleavage – overlayed by a generational divide – around the importance attached to the UK’s relationship with US and EU, with 48% regarding the UK-EU relationship as more important and 35% prioritising the UK-US one. At the same time, David Landsman, a former British diplomat and a senior adviser to the BFPG, emphasised how an “underlying bedrock” around UK and US collaboration on intelligence and security continued to come to underpin ties. “This is a relationship which does not look in bad shape, and with both being in lockstep going into Vilnius, it does look quite powerful, particularly when it comes to bolstering a message of staying the course in Ukraine,” he added. Ellwood welcomed the “robust and confident” relationship Sunak had developed after Biden placed the UK “on the naughty step” over the the Northern Ireland protocol. “He also saw a populism that resonated with what he was experiencing back in the US, and that aggressive, bombastic politics really wasn’t his cup of tea.”