Published: 8:18 AM November 18, 2019 Updated: 6:26 PM September 17, 2020

Peter Kellner, former president of YouGov, said "the Lib Dems have been boosted by their stance on Brexit, mainly at Labours expense. Photo: Anthony Devlin / PA - Credit: PA Archive/PA Images

A polling expert has predicted huge successes for one party in the country's capital as they make gains in marginal seats.

Peter Kellner, former director of YouGov and previously a BBC Newsnight reporter, said the Liberal Democrats are close behind the Conservatives who only hold "narrow leads" on a number of seats.

In new constituency survey conducted by the Observer analysing three marginal seats in London, the Lib Dems seem to be making massive gains against the Tories, such as in Finchley and Golders Green, where the Lib Dems have seen a 25% increase in voter intention placing them just 14 points behind the Tories, while Labour are predicted to receive only 19% of the share.

Elsewhere, in Kensington, the Lib Dems are only three percent behind the Tories holding 33% of the vote share, up 21% from 2017.

In Wimbledon, a 21% increase in support for the Lib Dems has seen them get within two points of overtaking the Tories, who are currently predicted to receive 38% of the vote.

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Kellner said these seats "are London marginals that overwhelmingly voted to stay in the EU in the 2016 referendum. In all three, the Lib Dems have been boosted by their stance on Brexit, mainly at Labour's expense".

He added: "Two years ago, Conservative support in these seats was evenly divided between pro- and anti-Brexit voters. Their support among Leave voters is rock solid; but Johnson's Brexit policy has gone down badly with many pro-European Tories. Around half of the party's Remain voters have deserted it. Most of this group now back the Lib Dems; there are also a number of ex-Tory Remain "don't knows" who have yet to decide how to vote

"Nevertheless, the Conservatives are currently leading in these strongly Remain seats, because the anti-hard-Brexit majority is divided between Labour and the Lib Dems."

In the poll, respondents were also asked how they would vote if they thought only two candidates had a 'realistic chance'. Most Labour and Lib Dem supporters are prepared to vote tactically, and most Labour supporters are willing to switch to the Lib Dems if it kept the Tories out.

"These surveys uncover the reasons why the tactical choices of Labour and Lib Dem supporters are different. Labour supporters are hostile to both Johnson and Brexit; a switch to the Lib Dems accords with both sentiments," Kellner said.

"Many Lib Dem supporters are more conflicted. They are almost exclusively anti-Brexit. But most are also hostile to Jeremy Corbyn, and in all three seats, most think the Tories would be better than Labour for the economy."