Andy Burnham has broken his silence after Labour’s leadership blocked his bid for MP selection in a political gamble that risked sparking civil war within the party.

The National Executive Committee (NEC), which is chaired by home secretary Shabana Mahmood and also includes Sir Keir Starmer among its members, rebuffed Mr Burnham’s application to become Labour’s candidate in the upcoming by-election in Gorton and Denton on Sunday. The vote was 8-1 against the mayor of Greater Manchester.

The decision has provoked backlash from MPs supportive of Mr Burnham, who said “deep-seated factionalism” was going to “destroy the Labour Party”, while some sections of the party claimed the move was a “stitch-up”. Former cabinet minister Louise Haigh said Labour should reverse the decision, and John McDonnell told the prime minister the move would “hasten your demise”.

The Manchester mayor wrote to the NEC on Saturday asking for permission to enter the process for selection for the forthcoming by-election. He said he wanted to run a “hopeful and unifying campaign” and promised to “support the work of the government, not undermine it”.