UKIP received "assurances" from Kate Hoey's campaign before standing aside in Vauxhall, it has been revealed.
Labour's sitting MP has in the past insisted she cannot control what UKIP does when asked about the hard right party's decision not to put forward a candidate to run against her.
But at a press conference this morning, UKIP'S economics spokesman Patrick O'Flynn claimed the two sides had been in contact - and Ms Hoey now had a duty to "stay true to the agenda and meet the assurances they have given".
He said: "Our branches have had conversations with sitting Conservative members, Labour members as well, in the case of Kate Hoey and Kelvin Hopkins, and Conservative candidates where a Brexit-supporting candidate is a narrow second to a remain MP.
They have been given assurances and I would suggest we’ve put our country before our party in standing aside in those seats. It does place a very heavy burden of responsibility on the people who will benefit from that to stay true to the agenda and meet the assurances they have given."
The details of the deal reached between Kate Hoey and UKIP have not been public, but in another constituency a candidate has pledged to meet with local UKIP members every 3 months.
Ms Hoey campaigned alongside then UKIP leader Nigel Farage in the run-up to last year's referendum - a position that puts her at odds with her constituents, with 78.6% of Lambeth voting Remain.
Liberal Democrat candidate for Vauxhall George Turner said: "This proves beyond doubt in Vauxhall a vote for Labour is a vote for UKIP."