LONDON (Reuters) - Former prime minister Theresa May urged her successor Boris Johnson to protect Britain’s values to help strengthen ties with the new U.S. administration, saying his threat to break international law had done nothing to raise “our credibility”. May, who said she “never knew what to expect” from U.S. President Donald Trump, described the inauguration of Joe Biden in an article in the Daily Mail newspaper as a chance for both countries to better promote democratic values. Britain’s former leader was herself criticised by some opposition lawmakers for being too close to Trump after he held her hand on a visit to Washington. But she has been outspoken in her criticism of Johnson since he replaced her in 2019. “The arrival of President Biden provides Britain with a golden opportunity,” she said in the article. “But to lead we must live up to our values,” she said, adding that threatening to break international law in talks with the European Union on a trade deal and moving away from defence and aid spending targets were “not actions which, in my view, raised our credibility in the eyes of the world”. Biden will be sworn in as the 46th president of the United States on Wednesday and the government hopes to reinvigorate ties with Washington, especially as Britain hosts a summit of the Group of Seven nations and the United Nations COP26 climate change conference this year. Asked in parliament about May’s article, Johnson said Britain had a “phenomenal year” ahead when it could show leadership, and that he would work closely with Biden. But Britain’s threat in last year’s EU talks to break international law in a post-Brexit arrangement for Northern Ireland was criticised by Biden at the time. He warned that a future U.S. trade deal would be in jeopardy if Britain failed to honour the 1998 Good Friday peace deal, which effectively ended 30 years of sectarian violence in Northern Ireland and was brokered with support from Washington. Johnson dropped the threat after agreeing alternative arrangements with the EU. “With Brexit now achieved but the pandemic still raging and the long-term economic and social impact of COVID to be addressed, it is now even more important that we work together with our allies,” May wrote.