Former Labour prime minister Gordon Brown has said that the UK, having previously been admired around the world for being inclusive and outward-looking, now presents a picture of division, intolerance and introversion.

In an opinion column for The Observer newspaper, Brown wrote that three weeks into Boris Johnson’s premiership, “English nationalism is on the rise, the Conservative and Unionist party has been reincarnated as the Conservative and Brexit party (and) unionism appears to be sleepwalking into oblivion”.

He added that the UK has sacrificed common sense to pursue a dogmatic abandonment of its own best interests.

Brown, who was prime minister from 2007 to 2010, said nationalism is pulling the UK apart, driving it towards “an unprecedented economic calamity precipitated by a no-deal exit from the EU”.

The former PM wrote that Johnson’s recent visits to various parts of the UK have done nothing to dispel the impression that under him the world’s most successful multinational state “is devoid of a unifying purpose powerful enough to hold it together and to keep four nationalisms – Scottish, Irish, English and also a rising Welsh nationalism – at bay”.

Brown, who is Scottish, also blasted the SNP, saying it is peddling what it claims is a progressive, pro-European Scottish nationalism while ignoring what he says are the hundreds of thousands of jobs at risk if Scotland leaves the UK.

He finished by saying that the ideals of an inclusive outward-looking Britishness “could not survive the divisiveness and chaos of a no-deal Brexit”.

To prevent the rise of dysfunctional nationalism, Brown said, “the first step is to stop no deal in its tracks”.