LONDON (AFP) - Prime Minister Boris Johnson vowed on Tuesday (Dec 10) to demolish three years of stalemate over Brexit, as Britain's political leaders geared up for a frantic final day of general election campaigning.

Mr Johnson ploughed a British flag-themed digger, marked "Get Brexit done", through a styrofoam wall with "gridlock" written on it, in a bid to ram home his core message in time for Thursday's snap vote.

Mr Johnson's centre-right Conservatives have been consistently ahead in the opinion polls, but YouGov's final survey of the campaign predicted they were set only for a narrow majority - with the race tightening.

The pollsters' seat projection put the Conservatives on course for a relatively slender 28-seat majority in Parliament's 650-member lower House of Commons - down from a comfortable 68 forecast by YouGov on Nov 27.

Mr Johnson's current Conservative minority government hopes to secure a majority that would let him pull Britain out of the European Union by the end of next month.

The new poll forecast that the Conservatives would take 339 seats (up 22 on the last general election in 2017), with the Labour main opposition on 231 (down 31).

The Scottish Nationalists are on course for 41 seats, up six, while the Liberal Democrats are set for 15 seats, up three.

YouGov interviewed approximately 100,000 panellists over the past seven days.

But it warned that the final number of Conservative seats could be between 311 - hung Parliament territory - and 367.

LAST PUSH

The main party leaders prepared to criss-cross the country on Wednesday in a last-ditch pitch for votes.

"However you voted in the EU referendum, your priorities have been ignored over the last three years whilst Parliament has been in gridlock - unable to focus on the issues that matter to you, because it was so busy arguing with itself about Brexit," Mr Johnson said.

Labour leader Jeremy Corbyn sought on Tuesday to exploit the Conservatives' perceived weakness on state healthcare and divert attention from his own mixed messages on Brexit.

But his push to narrow the poll gap was not helped by a leaked recording in which Labour's own health spokesman called the left-wing party's prospects "dire".

"It's abysmal out there," Mr Jonathan Ashworth said in a recording published by a right-wing website.

"They can't stand Corbyn and they think Labour's blocked Brexit."

Mr Ashworth told the BBC the tape was real, but he was speaking in jest.

Nonetheless, the Conservatives are worried about how Thursday could go.

An internal memo published by The Daily Telegraph newspaper warned that just 40,000 votes in 12 constituencies could see leftist Corbyn become Britain's next premier.

HEALTH SERVICE BATTLEGROUND

Mr Corbyn believes he can reach those voters by focusing on the state-funded National Health Service.

Labour claimed that nearly 4,700 deaths between October 2018 and November 2019 could be attributed to "patient safety incidents" caused by NHS staffing constraints.

"I blame the government that has underfunded our NHS," Mr Corbyn told supporters in central England.

Labour accuses Mr Johnson of abandoning the principle of free treatment for all by secretly plotting to open up the NHS to pharmaceutical giants in a new trade deal with US President Donald Trump.

Both Mr Johnson and Mr Trump deny the claims.

Surveys show the NHS being almost as important to voters as Brexit itself.

They also point to a general mistrust of Mr Corbyn's non-committal position on Brexit and frustrations over the Conservatives' handling of the NHS.

Mr Johnson has campaigned on his government's determination to "get Brexit done" and honour the result of the seismic 2016 referendum on EU membership.

Analysts suggested Labour's ability to keep the focus on health and other social issues could be vital for their prospects.

"This kind of last-minute thing, that really does ram home Labour's core message, at this point could nudge a few people in certain vital constituencies to vote Labour," University of Nottingham Professor Steven Fielding told AFP.

"It could be the difference between a majority Conservative government and a hung Parliament."

The Britain Elects poll aggregator puts the Conservatives on 43 per cent, Labour on 33 per cent, the Lib Dems on 13 per cent, and the Greens and the Brexit Party on three per cent each.