The booing of Boris Johnson at the Queen’s platinum jubilee celebration by large sections of a crowd – of royalty enthusiasts, who would not normally jeer a Conservative leader –has marked a turning point for the embattled UK premier. Three days later his leadership was put to a vote of confidence by his party’s MPs. Fewer than 60% backed him. Johnson survives – for now. Several scandals have rocked the Conservatives recently, causing a by-election defeat in a seat held since the 1830s and sending their poll ratings tumbling. The Labour Party has pulled ahead in opinion polls and its leader Ke…