Jeremy Corbyn’s team are banking on the election’s TV debates to tackle the Labour leader’s personal unpopularity and close the stubborn gap on the Conservatives, amid polling that suggests the Tories continue to enjoy a large double-digit lead.

Election 2019: London polls show surge to the Lib Dems Read more

Corbyn’s team believes that he is still being underestimated by the Conservatives going into the first televised debate this week, despite his success in reversing a large Conservative lead in the last election two years ago. A series of TV confrontations, with differing formats, will begin on Tuesday evening on ITV when Boris Johnson will take on Corbyn in a two-way head-to-head chaired by presenter Julie Etchingham.

The events will play a key part in influencing the decisions of millions of voters at the ballot box on 12 December, according to the latest Opinium poll for the Observer. Some 42% of voters questioned by Opinium said they were likely or very likely to watch at least one of the television encounters, with 43% of those saying the performance of the leaders would either be decisive or important in determining how they eventually make their decision.

Corbyn will need to use his television appearances to make up a large amount of ground on the Tories. According to Opinium, the Tories have stretched their poll lead and now have a 16-point lead over Labour. The Conservatives are up three points compared with a week ago, and now stand on 44%. Labour is down one point on 28%. The Liberal Democrats are also down one point on 14%, their lowest showing since August, while the Brexit party is unchanged on 6%.

With senior figures on all sides believing there has been little in the campaign so far to have cut through to voters, the debates have taken on further significance.

Facebook Twitter Pinterest Jo Swinson of the Lib Dems, who are aiming to lock in former Labour voters by promising to invest an additional £6bn in the welfare system. Photograph: Simon Dawson/Reuters

For the Tories, they are the best way to kill off any chance of a Labour revival of the kind that saw Theresa May lose a major lead in 2017. For Labour, they are a chance to showcase their popular spending plans on free broadband and the NHS – and demonstrate that Corbyn can hold his own against Johnson.

Bad A&E figures and criticism of Johnson after the Yorkshire flooding last week were a sign of the dangers faced by the Tories as they attempt to frame a simple message around resolving Brexit, boosting police numbers and investing in the NHS. The Tory manifesto launch this week is intended to instil further discipline into its campaign. Tory HQ has been boosted by the decision by some Brexit party candidates to pull out of key Labour-held marginals. However, it has been forced to deny claims from figures inside Nigel Farage’s party that some Brexit party candidates were offered jobs in return for standing aside. Ben Habib, a Brexit party MEP, told Sky News on Saturday that the Tories were “being economical with the truth” by denying the claim. He said: “It has been going on without a shadow of a doubt.”

He denied being approached himself, but said Ann Widdecombe had been “offered some sort of negotiating position with the Tory party – from Number 10”.

In a sign of the sheer volatility of the election, there is new evidence that the Lib Dems are surging in some of their key target seats – but have more to do if they are to overturn the Conservative lead.

In three closely fought London constituencies, the Lib Dems have seen spikes of more than 20 points. However, the Deltapoll surveys reveal that the Tories currently have a lead in the seats of Kensington, Finchley and Golders Green, and Wimbledon.

The seats are an important measure of the Lib Dems’ performance because the party has targeted strongly pro-Remain constituencies. And the Conservatives also know that losing some pro-Remain seats in the south-east could undermine their chances of securing a stable majority.

In Finchley and Golders Green, there has been a 25-point swing from Labour to the Lib Dems – but the party still remains 14 points behind the Tories. In Kensington the party is up 21 points, but the Tories are now three points ahead. In Wimbledon, Jo Swinson’s party is up 21 points, but remains two points behind the Tories.

Deltapoll questioned 500 electors in each constituency by telephone between 7 and 13 November. The data was weighted to be more representative and voting intentions were adjusted to take account of turnout.

The Lib Dems are attempting to lock in former Labour voters by promising to invest an additional £6bn a year in the welfare system over the course of the next parliament, as part of its manifesto launch this week. Some £2.6bn would be spent on abolishing the two-children limit on benefits and £220m on abolishing the welfare cap.