Theresa May rebukes Boris Johnson as UK welcomes Biden administration

British Prime Minister Boris Johnson welcomed the start of a new UK-US chapter on Wednesday under incoming US President Joe Biden, even as his predecessor Theresa May accused Johnson of abandoning the UK's moral leadership in the world during the tumultuous Trump era.

May, who resigned in 2019 amid turmoil over Brexit, has been critical of Johnson's handling of Britain's exit from the European Union. The open criticism is unusual because both prime ministers represent the Conservative Party.

Writing in the Daily Mail newspaper, May slammed Johnson's threat last year to breach the legally binding Brexit treaty he had signed with the EU, and his decision to abandon a commitment to spending 0.7% of Britain's GDP on foreign aid.

May said to lead we must live up to our values. Threatening to break international law by going back on a treaty we had just signed and abandoning our position of global moral leadership as the only major economy to meet both the 2 per cent defence spending target and the 0.7 per cent international aid target were not actions which, in my view, raised our credibility in the eyes of the world, May said.

Since Biden won the US election in November, Johnson has tried to shake off criticism that he became too close to outgoing President Donald Trump. The two men's populist, crowd-pleasing styles have often drawn comparisons.

Johnson's supporters argue that all British prime ministers have to forge strong relationships with the occupant of the White House. May was the first world leader to visit Trump after his inauguration in 2017, though their personal relationship was never warm.

Johnson has congratulated Biden and noted that they share priorities, including combating climate change and bolstering international institutions.

Johnson told the House of Commons that he looked forward to working with Biden and with his new administration, strengthening the partnership between our countries and working on our shared priorities from tackling climate change, building back better from the pandemic and strengthening our transatlantic security.