Former UK prime minister Theresa May accused her successor Boris Johnson of abandoning Britain’s “position of global moral leadership” and urged him as a leader to “live up to our values".
Writing in the Daily Mail to mark Joe Biden's inauguration as US president, Mrs May criticised Mr Johnson for threatening to break international law on Brexit and failing to commit to targets on defence spending and international aid.
These were “not actions which, in my view, raised our credibility in the eyes of the world", Mrs May wrote.
The arrival of Mr Biden gave the UK a “golden opportunity” to reset relations with the US and “play a decisive role in shaping this more co-operative world", she said.
Mrs May's comments come at a delicate time for Mr Johnson as he prepares to host two key global events this year: the G7 summit in June and the UN climate change conference in November.