A YouGov poll for the Sunday Times put the Tories on 47%, up two points on last month and 22 points ahead of Labour, which was unchanged on 25%. The Liberal Democrats were also unchanged on 18%.

However the ComRes poll for the Independent on Sunday suggested the Tories could have extended their lead even further if it was not for the shock decision to quit by former shadow home secretary David Davis.

Overall ComRes put the Conservatives on 44%, one point up on last month and 18 points ahead of Labour who were unchanged on 26%. The Liberal Democrats were down two on 17%.

But in interviews conducted before 1pm on Thursday, when Mr Davis announced that he was standing down to fight a by-election, support for the Tories was running at 48%. Afterwards it dropped to 41%.

:: YouGov interviewed 1,759 voters across Britain online on June 12 and 13. ComRes interviewed 1,012 adults in Britain by telephone on June 11 and 12.