Britain should adopt a more federal structure to guard against discontent turning to anger as standards of living fall after Brexit, says former prime minister Gordon Brown.

The senior Labour politician said wholesale reform of the UK was needed as the nation is united in name only, with a much greater degree of devolution required for Scotland, Wales, Northern Ireland and the English regions.

He said the strains of the vote to leave the EU were already beginning to show as different nations, regions, sectors and companies were “desperately seeking their own opt-outs from a hard Brexit”.

Brown said the optimism felt by leave voters in the north of England would in particular be short-lived as the region is more dependent on trade than the south.

“We could see discontent turn into anger as standards of living fall faster and jobs start to go,” he said. “It is clear that the UK in its present form is not working for everyone. To prevent the harmful divisions that now exist from deepening, we need to reimagine the UK for new times.”

To address inequalities in the UK, Brown called for EU powers over agriculture, fisheries, regional policies and social funds to be repatriated not to Westminster but nations and regions. More than half of the £4bn spent annually in the UK by the EU should be returned to local and devolved governments, he said.

He suggested the way to achieve this would be a people’s constitutional convention – an idea backed by Jon Trickett, a Labour frontbencher and election coordinator.

“A people’s convention is the starting point if we are to give fairness, hope and opportunity to the regions,” Brown said.

Some of his other suggestions include devolving employment law to Scotland, and creating co-decision for the four nations of the UK on fundamental issues so that Scotland, Wales and Northern Ireland would not be able to be taken out of the European convention on human rights against their will.