British prime ministers have been absent from the world stage for the past four years while becoming too close to Donald Trump and his “pie in the sky promises” of a free trade deal, a former UK ambassador to Washington has said. Sir Peter Westmacott, who was ambassador from 2012 to 2016 and got to know many of Joe Biden’s foreign policy team when they were working for Barack Obama in that period, said the start of the new US administration gave Britain a chance for a diplomatic reset, so long as ministers “bring bread to the table”. The modus operandi of British foreign policy had been hamstrung in the Trump years, Westmacott told the Guardian in an interview. “Britain’s first instinct, especially when it does not know what to do, is to ask the Americans, but that was near impossible when US policy was being made by early hour tweet,” he said. “There were also huge gaps in the Trump administration either because places never got filled, people resigned or got fired, leaving Britain with no one to deal with. An awful lot of western policymaking went by default, and that meant the gap was filled by others that were able to make hay.” In his new memoir, They Call It Diplomacy, spanning 40 years in the Foreign Office, Westmacott claims the chance of a post-Brexit trade deal with the US had an impact across UK foreign policy, especially in the Middle East. “Trump’s promises that after Brexit the UK would benefit immediately from a tremendous new free trade agreement with the United States were pie in the sky. But they led Theresa May and her successor, Boris Johnson, to give top priority to aligning British policy with that of the Trump administration,” he wrote. “Even before the new president had taken over, May’s government turned its back on the Middle East peace process initiatives which had been developed in close partnership with the UK […] Britain also joined the Americans at the UN security council in tabling draft language on Yemen, placing the entire responsibility for the war on Iran and its Houthi proxies without mentioning the suffering caused by the bombing of civilian targets by the Saudi and Emirati air forces.” Westmacott said a UK reset with the US would not be simple. “The impressions I got from my friends in the old Obama administration that are now being recycled in the Biden team was that there was a pretty strong sense that Brexit was a mistake, mis-sold, not in America’s interest, and that they had not forgotten some of the more colourful language used by Johnson towards some Democratic politicians. Nor had they forgotten the sucking up to Donald Trump,” he told the Guardian. “Nevertheless, whether it is due to nimble diplomacy or the nature of the beast, Biden and Johnson have got off to a pretty good start. But Britain has to put bread on the table. It has got to make a contribution on the issues that the US cares about. On the Iran nuclear deal, for instance, we have diplomats on the ground, unlike the US. Iran fundamentally cares about only one thing, its survival, so I think a deal is doable. “On Yemen, perhaps I am naive, [but] we can help. I am sure Biden cares about this issue a lot more than Trump ever did. The UN envoy is a Brit and we have a historic responsibility to the Aden protectorate. “Similarly, we can have a role in devising a multilateral approach to China. The UK is waking up, like everyone else, and realising China requires a collective approach. And on Russia, for whatever reason, Trump was in awe of Putin and not prepared to stand up to him. Biden, by contrast, sees him as a threat to democracy through cyber-attacks and suchlike, and there we have invaluable expertise. Through Nato we may be able to show that the Brits have got something serious to offer in terms of calibrating a serious security strategy.” Westmacott said it was already clear that the UK was trying to be active as president of the G7. This contrasted with the previous four years when, he said, the main refrain from friends from Europe to Asia was “where have you gone?” He cautioned Johnson not to be tempted into trying to disrupt or even goad the EU, arguing it was not the kind of UK-EU relationship that the Biden team would want and was not in the UK national interest. He believes the UK foreign and security leaders overall have recognised that their leverage will be enhanced if they cooperate with the main European players, albeit initially on ad hoc basis. “With the world as unpredictable and unstable as it is, not least because of all the unpredictability and flip-flops in the US over the past four years, it is in the UK’s interests to re-establish working relationships on foreign policy with the other principal capitals of Europe,” he said. He sees the US and the UK’s joint recent absence as coinciding not just with China’s rise but also a realisation that China’s economic strength was not leading to political and social reform. “We need to think again, and make them realise they have got to play by the same rules as us,” he said. “They have certainly got a very big interest in the survival of the western economy that they want to dominate. They have got trillions of dollars of US debt, and they don’t want to destroy the west in the way that Putin does.”