Andy Burnham has said he will not “abandon the responsibility” of fighting the climate crisis after the government approved the Jackdaw gasfield, pledging to block new North Sea licences and keep Britain on track for net zero by 2050.

The comments are the prime minister’s most forthright yet on net zero, after many MPs have privately cast doubt on the authenticity of his commitment to tackling the climate crisis.

The energy secretary, Miatta Fahnbulleh , insisted that she alone would make a decision on whether to approve the Rosebank oilfield – a decision sources say she is minded to block.

Burnham has been under pressure from industry and political opponents, as well as some Labour MPs, to water down Labour’s manifesto promises on new oil and gas licences and the net zero targets.

“There has been much speculation about what this announcement means for Britain’s commitment to addressing the climate crisis.…