Since Boris Johnson became Prime Minister after being declared party chief by Tory members, the Conservatives have gained 10 points to stand at 30%, a survey by Deltapoll for the Mail on Sunday showed.

That puts them five points ahead of Labour at 25%, with the Liberal Democrats on 18% and the Brexit Party on 14%.

But if Labour was to drop Jeremy Corbyn as leader, the poll says the party would shoot into the lead at 34%, with the Tories on 28%, the Brexit Party on 14% and the Lib Dems on 13%.