Boris Johnson's popularity plummets after conference speech attacking Theresa May

Former foreign secretary Boris Johnson has seen his popularity plummet amongst Conservative voters and Leave backers, according to a new poll.

The amount of people who view him positively has declined steeply since his speech at his party’s conference, with a YouGov tracker stating his net favourability has gone to -35.

It had been -28 on the eve of him addressing the crowds, while Prime Minister Theresa May’s is at -22.

A post from YouGov said: “Worse still for the Chequers-slamming Tory rebel, the change seems to have come primarily among Conservative and Leave voters.”

Among Conservative voters, 44 per cent hold a favourable view of Mr Johnson, while 48 per cent hold an unfavourable view.

In his speech at a fringe event at the Conservative conference, Mr Johnson attacked Mrs May and her so-called Chequers plan.

He said: “If we cheat the electorate — and Chequers is a cheat — we will escalate the sense of mistrust,” Mr Johnson declared to a crowd of 1,500 Tory activists , media and visitors crammed into a side hall.

“And I am afraid we will make it more likely that the ultimate beneficiary of the Chequers deal will be the far-Right in the form of Ukip.”

Mr Johnson timed his arrival in Birmingham to coincide with a keynote address by his reputed leadership rival Sajid Javid. This meant the Home Secretary addressed a half empty 3,000-capacity main hall.

On Monday, Mr Johnson took aim at Labour leader Jeremy Corbyn during a session in the Commons.

He blasted him over what he called a “shameless U-turn” with his decision to back a customs union amidst ongoing Brexit negotiations.

Mr Johnson said: "In deciding to remain in the customs union, [Mr Corbyn] is guilty of a shameless U-turn and a betrayal of millions of people who voted Leave."