The Conservative lead in the general election campaign has been more than halved in just one week, putting the UK in “hung parliament territory”, an exclusive poll for The Independent shows.

Boris Johnson’s party is now only six points ahead of Labour, it has found – matching other surveys suggesting the race is tightening dramatically, amid growing Tory nervousness.

Jeremy Corbyn is successfully winning back the support of voters threatening to defect to other parties, the poll by BMG Research shows, taking his party’s rating up five points to 33 per cent.

The Conservatives, meanwhile, have dipped two points to 39 per cent, six points ahead instead of the 13 points in BMG’s survey a week ago.

Crucially, polling experts believe a lead of at least six points will be needed to deliver the Commons majority Mr Johnson is seeking – and his Brexit deal in January.

Robert Struthers, BMG’s head of polling, said there was growing evidence Labour is “starting to build momentum” ahead of the election on 12 December.

“The shifts we have witnessed in our headline voting intention figures take the Conservative lead from a likely majority into possible hung parliament territory,” he said.

The results come at the end of a week when Mr Johnson has faced a torrent of criticism over everything from his previous attacks on single mothers and working class men to ducking out of a grilling by Andrew Neil.

In the wake of the London Bridge terror attack, the prime minister faced difficult questions over the early release from prison of the attacker, although the BMG research was carried out before the atrocity.

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Tory strategists are worried the arrival of Donald Trump for a Nato summit in London on Tuesday is a moment of potential danger, fearing what the unpredictable US president will say or do.

On Friday, Mr Johnson took the highly unusual step of urging him not to intervene in the election campaign – knowing his backing would backfire – and the pair are unlikely to hold a face-to-face meeting.

The BMG research shows the Liberal Democrats continuing their slide, down five points, while the Brexit Party is marooned on just four per cent, behind the Greens on five per cent.

Jo Swinson’s party had hoped to scoop up most Remain voters from the 2016 referendum, but the poll shows more drifting to Labour – 46 per cent, up from 39 per cent last week.

The Conservatives are worried the Lib Dems’ troubles are leading to the Remain vote coalescing behind Labour and its promise of a Final Say referendum.

Vince Cable, the former Lib Dem leader, criticised his party’s policy of revoking Article 50 – now all but ignored in its campaign – as always “wildly improbable”.

“We were never going to get 350 MPs, so the policy had been and should be to argue for the people’s vote, going back to the public, to the referendum with support for Remain,” he said.

Mr Struthers pointed to Labour voters coming home, with 73 per cent of those who backed the party at the 2017 election now planning to do the same on 12 December – up from 67 per cent a week ago.

In contrast, the Tories had “less room for growth”, having already banked most Brexit Party supporters, after Nigel Farage’s decision to pull out of Conservative-held seats.

Mr Johnson’s party is backed by 70 per cent of Leave voters, and although Labour has attracted only 17 per cent, that figure is up four points in a week.

“The key question for the remainder of the campaign is the extent to which Labour can continue to squeeze the Liberal Democrat and Green vote,” Mr Struthers said.

“If this trend continues, this election could be much closer than it looked just a matter of weeks ago.”