‘This is the day the Scottish left came out of its ghetto,’ Robin McAlpine, the director of the Jimmy Reid Foundation, said towards the end of last month’s Radical Independence Conference (RIC) in Glasgow. Around 800 people had paid £10 a head (£4 unwaged) to listen to speeches from socialist and green politicians, trade unionists and disability activists in the rather incongruous setting of the Radisson Blu hotel near Central Station.

In the morning, Dennis Canavan, the former Labour MP for Falkirk West, said that ‘independence is a great opportunity for radical politics.’ Canavan, who was rejected as a candidate for the inaugural Holyrood elections by New Labour and subsequently won a seat as an independent, characterised himself as ‘not a nationalist’ but ‘an internationalist’. It was a distinction that recurred throughout the day: at one workshop I attended, a young Socialist Workers Party cadre called for an ‘internationalist Scotland’ and ‘workers’ unity’.

In the fissiparous world of Scotland’s radical left, independence is an issue most can agree on. Many are retracing a journey made by Jimmy Reid himself; the leader of the Upper Clyde Shipbuilders Work-In, who died in 2010, went from the Communist Party to the SNP via two decades in the Labour Party. (A notable absence from the RIC was that of another former Labour dissenter, Tommy Sheridan.)

For decades, Scots voters have been at odds with their English counterparts, consistently returning a majority of Labour MPs and ever fewer Conservatives: there is now only one, David Mundell, the MP for Dumfriesshire, Clydesdale and Tweeddale (as one slogan that came out of the RIC put it, ‘David Cameron is a one nation Tory; we’re a one Tory nation’). Having shrugged off the ‘Tartan Tory’ moniker, the SNP has carved out an ostensibly social democratic agenda at Holyrood that, it claims, would be strengthened under independence. At the same time, as one Glasgow activist put it, revolutionaries have come to ‘think we have a chance of overthrowing Edinburgh more easily than London’. (Though it’s also possible that an independent Scotland would turn out to be a low-tax free-market economy.)

The RIC came just over a month after an unusually restive SNP annual conference, which saw the party, by a slim majority, overturn its historic opposition to Nato membership. Two MSPs resigned from the party in the wake of that decision. A number of SNP members and elected representatives were at the RIC. Alex Salmond, once suspended from the SNP for belonging to the leftwing 79 Group, issued a rather circumspect press release, welcoming ‘voices to the left of the SNP’s social democratic position’ as well as ‘support for independence from the entrepreneurial and more free-market perspective’.

The SNP has been accused of being over-cautious, of presenting independence not as a radical change but as a form of continuity: Scotland will keep the queen, the pound and the welfare state. ‘How can you achieve independence without articulating a radical vision?’ Patrick Harvie, the leader of the Scottish Greens, asked at the RIC. He went on to outline policies on banking reform, decentralisation and setting up a state-led energy company to meet Scotland’s ambitious green energy targets The loudest cheers of the day were reserved for anti-nuclear and anti-Nato declarations.

A broad Left-Green pro-independence platform appears to be coalescing. None of the parties represented at the RIC have a significant electoral voice (the largest of them, the Greens, has just two MSPs), but their vision of an independent Scotland based on social justice and green economics could deliver crucial votes in the referendum. How the movement will fit into the SNP-dominated architecture of the Yes Scotland campaign remains unclear: despite repeated protestations to the contrary, the SNP appears reluctant to accommodate such independently-minded groups. This will have to change. It is hard to see how the success of the 1997 devolution campaign could be repeated in 2014 without a similarly loose, big-tent approach.

To win, McAlpine said, the Yes campaign must convince three (overlapping) groups: women, public sector workers and Labour voters. Labour remains firmly opposed to independence, but the recently formed Labour for Independence appears to be attracting support. Last week, the Labour-dominated Scottish Trade Unions Congress refused to back Better Together, the official No campaign.