By William James, Andrew MacAskill and Alistair Smout LONDON (Reuters) -British Prime Minister Boris Johnson apologised to parliament on Tuesday after he was fined by police for breaking lockdown rules, saying he did not know a birthday gathering at the height of the pandemic was in breach of the rules he had set. Opposition lawmakers argue that the prime minister must go, saying he set stringent rules during COVID-19, broke those rules in Downing Street and then repeatedly lied to parliament when he said all guidelines had been met. Johnson told the House of Commons he had not deliberately mi…