The former Labour Prime Minister blasted his Tory successor in Downing Street, saying Mr Cameron had failed to deal with the fears of English voters around sovereignty and immigration in the run-up to the 2016 Brexit referendum,
In an excoriating speech at the Edinburgh International Book Festival today, Mr Brown claimed Scotland was now "trapped" between competing English and Scottish nationalisms.
Laying out how he believed a no-deal Brexit could be stopped, he said that he did not believe English voters who chose Leave on the ballot paper were "British or English nationalists", but that "Nigel Farage was" and Boris Johnson "comes close to that position and a lot of the Conservative backswoodmen are taking that position and that is the ideology dominating the British political system."
He added: "Voters in the north who felt neglected, not listened to, who wanted a change and they saw Brexit as a means for that and I'm trying to understand what lay behind it.
"David Cameron, let's be honest, could have negotiated a far better deal with the EU that could have dealt with people's fears about immigration and sovereignty.
"Look, in Germany you can't be an immigrant into Germany unless you're registered for work, you can't stay in Belgium after nine months if you haven't got a job, in France you can't be paid Latvian wages if you're a Latvian working in France.
"He could have done all those things, he could have dealt with some of the concerns people had about wages and everything else, he could have dealt with sovereignty question, he could have had a law passed in Parliament that said any ruling of the European Court that offended the principles of the Treaty of Maastricht, which required national identity to be taken into account, would not be accepted in the British isles if it offended these principles."
To resounding applause, Mr Brown he added: "He could have done all these things, but they were lazy, they thought they would win it without a fight - they didn't even put the right arguments, they didn't put a positive case for Europe and that's why we're in this position."
Mr Brown's appearance at the book festival marked the latest in a series of interventions by the former Labour Prime Minister on Brexit and Scottish independence.
In the past week he has weighed in on the "self-indulgent" prospect of a government of national unity led by Jeremy Corbyn, calling it a "waste of time", and urged opposition party leaders to speak to Brussels direct to shift the Brexit deadline of 31 October.
And he has also called for Parliament to commission an independent inquiry into the possible consequences of a no-deal Brexit.
Today he said Scotland was "trapped between two extremes" - the anti-European conservatism of Boris Johnson, and the "hardline separatism" of the SNP and that both nationalists and unionists "must both answer a simple question: what best meets the needs and aspirations of the Scottish people?"
He said that a "modern case for the Union" had to be made, and needed to be based on more than its longevity - "that the Union endures because it exists and it exists because it endures".
"Our case for the future needs to be built on the lasting virtues of empathy, reciprocity and solidarity between people," he said.
"The vast majority of us are proud Scottish patriots who love our country and its institutions and most of whom would not describe ourselves as nationalists who see life only in terms of a never-ending struggle between an ‘us’ and a ‘them’.
"The starting point of a modern union is that promoting co-operation between Scotland and England within the UK will achieve far more than a seemingly endless confrontation between Scotland and England."
Mr Brown's appearance was also a soft launch of a new think tank, Our Scottish Future, which will hold its first seminar this week looking at the potential currency options of an independent Scotland and their impact on poverty.
The think tank will, said Mr Brown, "encourage debate and publish information; with a view to demonstrating how the strong Scottish desire for change can be best met by a positive, patriotic and progressive alternative to the SNP’s narrow nationalism".
He said it would also show "how the Scottish Parliament can best be re-shaped as a far more effective force for economic progress, equal opportunity, social change and a fairer Scotland".
Speaking to a packed tent, Mr Brown referenced George Orwell's take on the differences between patriotism and nationalism. And he said a new Hope not Hate poll showed that 45 per cent of Scots agree and only 19 per cent disagree the new Prime Minister will sacrifice the Union for Brexit.
He added: "But if Johnson’s Conservative Party cannot re-unite a divided Scotland, then neither can the SNP which, since its April conference, is now pursuing a hard, not soft, version of independence - abandoning the UK customs union and single market and ditching the UK pound."
He said Scotland and the UK needed to accept that "we are in an interconnected and integrated world, where any country’s independence is limited by its interdependence and if the SNP applied the logic that has led them to support sharing sovereignty inside the European Union and were not obsessed by ending all connections with their neighbours in England, there would be a settled Scottish consensus in favour of a modern UK constitution that would balance the national autonomy Scots people desire with the cross border co-operation that we need".
The former prime minister also said the Scottish Parliament had to be stopped being used as a "battering ram" for constitutional warfare. "The time has come to argue for change: a Scottish Parliament acting explicitly and effectively as a genuine force for social, economic and educational progress," he said.
Hitting back at his remarks, SNP MSP George Adam said Mr Brown's "monthly interventions were becoming increasingly detached from reality".
He said: “The reality is that Gordon Brown would prefer the imposition of a disastrous Tory Brexit on Scotland over independence, which makes him every bit as extreme as the politics he purports to oppose. “For him, it is the union at all and any cost, which puts him increasingly on the wrong side of Scottish opinion. Scotland now faces a clear choice over its future – as an outward-looking, independent country or shackled to an insular Westminster, with right-wing Brexiteers like Boris Johnson running the show."Labour in Scotland is an increasingly irrelevant force – and people simply do not believe they can stand up to the Tories."