The Brexit Party leader Nigel Farage announced on Monday, 11 November, he would not be fielding candidates in 317 seats where the Conservatives are the favourites to win.
Instead Farage will target Labour MPs especially in seats in Wales, the Midlands and the North of England.
Political analysts were quick to seize on the significance of the announcement, saying Farage had effectively gifted the election to the Conservatives.
The announcement is a big blow to Jeremy Corbyn and Labour but could also hit the Liberal Democrats’ chances of picking up seats from Tory MPs who faced losing votes to the Brexit Party.
Conservative Party chairman James Cleverly welcomed the move, saying the Brexit Party had recognised they risked creating another hung Parliament which would prevent a “stable majority government".
Labour Party chairman Ian Lavery said it now meant there was effectively a "Nigel Farage and Boris Johnson alliance with Donald Trump to sell out our country."
Mr Lavery said: "We urge voters to reject this Thatcherite 1980s tribute act, which would lead to more savage Tory attacks on working class communities. Our NHS is not for sale.”
Last month Farage had urged Johnson to agree an electoral pact but the prime minister refused to do so.
There has been no word about whether the Tories and the Brexit Party have made a formal pact.
Farage had initially promised to field 600 candidates but he claimed his reason for changing his position was because Boris Johnson had committed to signing a trade deal with the EU which would be without "regulatory alignment" and would be similar to the deal Canada has with Brussels.
Farage said this was a "huge change" in the Conservatives' approach to Brexit.