The Liberal Democrats will target pro-Remain Conservative voters and Labour supporters in the final days of the Richmond Park byelection campaign, as party officials claim the race is tightening.

The latest data collected on the doorstep by the Lib Dems has Zac Goldsmith leading their candidate, Sarah Olney, by 46.7 per cent to 43.3 per cent.

After speaking to an estimated 40 per cent of eligible voters – and based on a predicted turnout of 60 per cent – Mr Goldsmith would win by just over 1,600 votes, down from a majority of 23,015 in May 2015.

The Lib Dems have said voter tracking data shows Ms Olney’s vote has been steadily rising throughout the campaign, increasing sharply after November 17.

At about the same point the number of undecided voters fell steeply.

Mr Goldsmith’s share of the vote has remained steady at about 46 per cent since the same period.

The internal Lib Dem memo read: “(Zac Goldsmith’s) vote is very hard but he is not gaining any significant support outside of that core base.

“Whilst hardcore Zac Goldsmith supporters are off the table, a much bigger pool of traditional Conservative – mostly Remain voters – are open to us.

“Voter modelling confirms that the key remaining undecided voters are traditional Conservative supporters who are pro-Remain.

“Unprompted they raise Brexit as the deciding issue for them and they are positively engaging with our campaign on this issue.”

Mr Goldsmith backed Brexit in the referendum, whereas Richmond Park and North Kingston voted 72 per cent in favour of Remain.

In a bid to win voters, the Liberal Democrats have made more than 94,000 attempts to speak to voters, from an electorate of about 82,500.

However many constituents have said they have been annoyed by the “bombardment” of campaign literature.

The Liberal Democrats also identified too many “Lib Dem/Labour waverers”, especially in the Canbury district of Kingston, as a problem.

The party memo read: “These Labour voters could hand victory to Zac Goldsmith if we cannot persuade them to vote tactically.”

A spokesman for Zac Goldsmith's campaign said: "This byelection is happening because Zac Goldsmith kept his promise to his constituents.

"The people of Richmond Park and North Kingston must now decide who they want to serve as their community champion, leading campaigns in Parliament on their behalf and working constructively with Government to get the best deal, for years to come.”