Boris Johnson may have told wavering Tory voters to help avoid a landslide Labour victory during his surprise, sole appearance on the campaign trail on Tuesday night.

But even the former Prime Minister’s father has admitted he will cast a ‘tactical vote’ for the Liberal Democrats today.

Stanley Johnson, a former Conservative MEP, said he wanted to boost Ed Davey’s party in his constituency due to their views on the European Union and the environment.

Admitting Boris would probably accuse him of ‘apostasy’ for his crime, he said he would back Helen Baxter in the Queen’s Park and Maida Vale constituency.

The latest YouGov polling shows the Liberal Democrats finishing third in the seat, just ahead of the Tories, with the Greens in second and Labour winning the contest comfortably.

Boris Johnson's father Stanley (pictured) has pledged to give his vote to the Liberal Democrats in a tactical move despite being a former Conservative MEP

Boris Johnson's father Stanley (pictured) has pledged to give his vote to the Liberal Democrats in a tactical move despite being a former Conservative MEP

In Mr Johnson's Queen¿s Park and Maida Vale constituency, the Lib Dems (leader Ed Davey seen) are polling in third, behind the Greens and Labour

In Mr Johnson's Queen’s Park and Maida Vale constituency, the Lib Dems (leader Ed Davey seen) are polling in third, behind the Greens and Labour

‘There I was coming out of the Underground station at Queen’s Park and there was this lady called Helen Baxter and she had her voting card and so on,’ Mr Johnson told the Telegraph.

‘I said to her one of the things which has upset me most of all in this campaign is the fact that two crucial issues, first Britain’s relationship with Europe, and second, the whole question of - and this links to the first of course - the environmental policy, have not had the airing they deserve.

‘And she said, well actually the Lib Dems do indeed have a strong policy on both these issues, and she presented me with her card, and yes, lo and behold, the whole third part of her programme was exactly Europe. So then I said to myself, well why should tactical voting not play its part here?

‘I’m a dyed in the wool Conservative, but in this particular case what matters is to try and boost the Lib Dems in a constituency which the Tories have absolutely no chance to win.’

The Conservative party constitution does not explicitly ban members from voting for other parties.

Ms Baxter said: ‘Boris Johnson’s dad is voting for me, the Lib Dem candidate in Queen’s Park and Maida Vale and agrees with us about the damage caused by his son’s disastrous Brexit.’