LONDON (Reuters) – London Mayor Sadiq Khan on Tuesday demanded an explanation from the capital’s Metropolitan Police force over how they decided who to fine for events in Prime Minister Boris Johnson’s offices that broke COVID-19 lockdown rules. New photographs of Johnson at a leaving party in Downing Street in November 2020 were published by ITV News on Monday, reigniting opposition accusations that he breached his own COVID-19 lockdown rules and calls for his resignation. Johnson was not fined for that gathering, but did receive a fine for another event, a party for his birthday in June 2020…