Ukip chose not to put up a candidate in Hampstead and Kilburn as part of a national strategy to avoid damaging “the Brexit cause”.

Ham & High: Giles Game. Picture: Giles GameGiles Game. Picture: Giles Game (Image: Archant)

The party won 1,532 votes in the constituency in 2015, more than enough to decide the outcome of such a marginal seat.

Ukip North London leader and Holborn and St Pancras candidate Giles Game told the Ham&High the constituency was “identified internally” as a seat where the party’s interests were best served by withdrawing their candidate.

He said: “There are places in which it was felt that our putting someone up might damage the Brexit cause, which remains our primary raison d’etre.

“My lack of surprise at this at the time was based on a couple of obvious points. First, when you look at the results for the last two elections, and particularly 2010 when Glenda Jackson won the seat with the narrowest majority in the country, Labour seem to have owed something to Ukip.”

Ham & High: Claire-Louise LeylandClaire-Louise Leyland (Image: Archant)

Mr Game added that he does not believe the party is endorsing another candidate in Hampstead and Kilburn, but since the only two pro-Brexit figures standing are Conservative Claire-Louise Leyland and famous Hampstead squatter “Rainbow” George Weiss, it appears likely the Tories will benefit from Ukip’s absence.

Labour’s candidate Tulip Siddiq, Mr Game said, is a “true Remainiac”.

“The current incumbent [Ms Siddiq] actually went so far as to vote against the triggering of Article 50 this year at the expense of occupying a shadow front bench position,” he added.

“We could almost certainly have found a candidate for Hampstead so it is a shame in a way – but there is I think some logic here.”

On Wednesday, Camden Greens decided to stand a candidate in the constituency after Labour refused their offer of a “progressive alliance”.

The deal would have meant the Greens – who won 2,387 votes in 2015 – stepping down and backing Labour in Hampstead and Kilburn in return for Labour stepping down in the Isle of Wight and Brighton.

Ms Siddiq’s majority in 2015 was 1,138 votes.