A pledge by Labour’s shadow chancellor John McDonnell that a future Labour government would not block a second referendum on Scottish independence has divided an already fractious opposition.

On the one hand, McDonnell’s statement potentially opens the way for a new pro-Remain coalition government, committed to a left-of-centre political programme. On the other, it opens the possibility that Scotland may leave the UK.

On Monday, the Labour Party’s deputy leader, Tom Watson, spoke out against a second Scottish independence referendum, prioritizing anti-austerity politics.

“We can see the mess caused by the prospect of the UK leaving the four-decade-long union with Europe – imagine how much more disruptive it would be to break our three centuries-long Union of Scotland within the UK.”

In voicing his objection, Watson is in line with the position of the leader of the Scottish Labour party, Richard Leonard, who has campaigned against Nicolas Sturgeon’s Scottish National Party (SNP) government on a unionist platform.

Meanwhile, the former Scottish Labour prime minister, Gordon Brown, has warned against giving way to nationalism in UK politics. In an open letter published by the Observer, Brown blamed warned that the ideal of tolerant Britishness “could not survive” a no-deal Brexit, as the UK would be devoid of a unifying purpose powerful enough to hold it together and to keep Scottish, Irish, English, and Welsh nationalism at bay.

A recent opinion poll suggests that 63% of Conservative party members prioritise leaving the EU over preserving the union, with regards to both Scotland and Northern Ireland.