By William James and Kylie MacLellan LONDON (Reuters) -An inquiry into COVID-19 lockdown-breaking parties at Prime Minister Boris Johnson’s office and residence said on Monday some of these should not have taken place, and serious failures of leadership and judgment occurred at the heart of the British government. Johnson is facing the gravest threat to his premiership over the parties at Number 10 Downing Street, and the report by senior civil servant Sue Gray had the potential to trigger an end to his premiership. However, parts of the report were not published due to an ongoing police inves…