Boris Johnson will go into the final full day of campaigning looking to win “every vote” after a fresh poll suggested a hung parliament could still be on the cards.

YouGov’s constituency-by-constituency poll predicts the Conservatives are on course for a 28 seat majority – but the margin of error and unknown impact of tactical voting means a hung parliament is still a possibility.

The pollsters, who have analysed more than 100,000 voter interviews over the past week, predicted the Tories will win 339 seats and Labour 231.

General Election 2019 opinion polls(PA Graphics)

A 28-seat majority would be the best Tory result since Margaret Thatcher’s showing in 1987 – but it is down from the sizeable 68-seat victory that the same YouGov-style poll had been predicting only two weeks ago.

Chris Curtis, YouGov’s political research manager, said: “The margins are extremely tight and small swings in a small number of seats, perhaps from tactical voting and a continuation of Labour’s recent upward trend, means we can’t currently rule out a hung parliament.”

The result will be a worry to Mr Johnson as he prepares for a final blitz across the country as the campaign enters its final full day, with Tory gains off Labour reduced from 44 to 29 since the November 27 findings.

The Tory leader told journalists at an event at JCB’s Cab Manufacturing Centre in Staffordshire he was “absolutely not” guaranteed victory on Thursday

“This is a very close fought election and we need every vote,” he said.

General Election 2019Prime Minister Boris Johnson drives a Union flag-themed JCB, with the words “Get Brexit Done’ inside the digger bucket, through a fake wall emblazoned with the word “Gridlock’, during a visit to JCB cab manufacturing centre in Uttoxeter, while on the General Election campaign trail (Stefan Rousseau/PA)

Mr Johnson will spend the final day of campaigning in Labour marginals in Yorkshire, the Midlands and Wales, before finishing the day with a rally near London.

While the polls have improved for Jeremy Corbyn’s Labour Party, the haul of 231 seats would mean a loss of 31 seats compared to 2017’s outcome – its worst result since the 1980s.

According to YouGov, Labour could be set to make two gains, pulling off a Cabinet minister scalp by taking Chipping Barnet, the constituency currently held by Environment Secretary Theresa Villiers.

Foreign Secretary Dominic Raab is in trouble to the Liberal Democrats in Esher and Walton, while former Tory leader Iain Duncan Smith in Chingford and Woodford Green is clinging on by only two points against Labour, the poll result indicates.

Putney could also go red but YouGov continues to predict a tough time for Labour in its heartlands in the North and Midlands.

Veteran MP Dennis Skinner’s Bolsover seat could be taken by the Tories, as could constituencies such as Great Grimsby, a Leave-voting town represented by Labour since the Second World War.

Corbyn pollLabour leader Jeremy Corbyn joins a phone banking session with party activists at the Scottish Labour Party headquarters in Glasgow (Jane Barlow/PA)

The SNP would win 41 seats – up by six – and the Liberal Democrats 15 if the prediction bears out.

Plaid Cymru would hold onto its four constituencies and the Green Party its one, while Nigel Farage’s Brexit Party would finish the election empty handed,  polling predicts.

YouGov uses multilevel regression and post-stratification (MRP) to form its predictions – a model that predicted 93% of constituencies correctly in the snap election two years’ ago.

The polling company first models voting preferences based on age, gender, education and previous votes, along with local political circumstances, before applying MRP, a technique which adds local factors and individual characteristics of each of Great Britain’s 632 constituencies to come up with its final result.

The poll results followed a day full of twists and turns on the campaign trail in which:

–  Shadow health secretary Jon Ashworth said he was “stitched-up” by a Tory-supporting friend after his comments calling Labour’s election chances “dire” were leaked.

–  Mr Johnson re-emphasised his promise of toughening prison sentences for violent criminals.

–  The PM faced further criticism from the father of Fishmongers’ Hall victim, Jack Merritt, for using his son’s death to “score some points in the election”.

–  Labour’s Mr Corbyn revealed his first act on entering Downing Street would be to allocate emergency funding for more hostel places to help those sleeping on the streets.

Mr Ashworth was recorded saying the situation facing Labour was “abysmal” because voters “can’t stand Corbyn” and think the party has “blocked Brexit”.

He told LBC radio during an evening phone-in on Tuesday that he had been “taking the piss” with his friend.

Ashworth leakShadow heath secretary Jonathan Ashworth (Andrew Matthews/PA)

The senior opposition figure said he thought the recording had been planned and that he’d been “stitched-up like a kipper”.

His leader Mr Corbyn said the health spokesman had his “full support” but refused to commit to keeping him in his top team after the election was over.

Mr Corbyn is expected to tour the Midlands and Yorkshire on Wednesday in a final attempt to deny the Tories an overall majority.

In a hard-hitting interview with Sky News, Dave Merritt – father to 25-year-old son Jack who died alongside Saskia Jones, 23, in the attack by Usman Khan during a prisoner rehabilitation near London Bridge last month – accused Mr Johnson of having “exploited” the tragedy.

Mr Johnson did not back down in the aftermath of the interview, however, instead telling the Daily Telegraph how he would look to extend jail terms for violent criminals.

He told the right-leaning newspaper the justice system “isn’t delivering” and that it was still “too weak” when handling the worst offenders.

Mr Johnson also revealed the six-weeks of living on the road during the campaign had taken its toll more than just politically.

He told a Sun-reading family in marginal seat Darlington: “I am so fat, I must lose weight”.

The Prime Minister also hinted he could propose to girlfriend Carrie, telling the Parker family he was “very happy” with the 31-year-old.