Boris Johnson's popularity among Tories and Brexiteers sinks to lowest level after conference speech attacking May

Boris Johnson's popularity among grassroots Conservatives and Brexiteers has sunk to its lowest level, in the wake of his dramatic conference speech attacking Theresa May's Brexit strategy.

A new YouGov poll shows the ex-foreign secretary's favourability ratings have slumped from -22 in early September to -28 a month later, before plummeting to -35 after his address to activists in Birmingham, where he urged Ms May to "chuck Chequers".

Mr Johnson resigned from the cabinet in July in protest over the prime minister's Brexit approach and he has done nothing to dampen widespread speculation over a possible leadership bid.

However in a blow to the leading Brexiteer, the new poll found his standing among Tory voters has fallen from +26 at the beginning of September to +6 a month on, and -4 after his much-hyped conference speech.

Among Leave voters, that score has fallen from +25 to +12 and now -1 over the same time period. Of those, some 45 per cent have a favourable view of Mr Johnson and 46 per cent have an unfavourable one, according to the poll.

Over the same period, Ms May's score has marginally improved from -23 to -22 among the general public, despite the rocky trajectory of the Brexit talks.

YouGov's Matthew Smith, the study author, said: "The speech given by Boris Johnson may have been covered just as closely by the press, and the former foreign secretary’s head may adorn the top half of the Daily Telegraph on a weekly basis, but neither of these things seem to be doing him much good."

The pollsters also found an increase in the proportion of people who viewed Jacob Rees-Mogg in an unfavourable light, as he became more well-known.

Some 18 per cent approved of the Brexiteer in September 2017, rising incrementally to 19 per cent in January and remaining at 19 per cent today.

By contrast, the proportion who disliked him rose from 30 per cent last year to 38 per cent in January and 46 per cent now - meaning his net favourability went from -12 to -19 and now to -27.

The trend was mirrored among Conservative voters, but Mr Rees-Mogg still enjoyed popularity among Brexiteers.

Mr Smith said: "Only among Leave voters has greater familiarity not necessarily bred exclusively greater contempt.

"Favourable views of Rees-Mogg have seen a modest increase from 29 per cent to 37 per cent over the time period, although unfavourable views have grown at a slightly faster rate – from 19 per cent to 31 per cent."