IN a pamphlet published today by the Fabian Society, “Progressive Federalism: a new way of looking at the United Kingdom,” Professor Jim Gallagher addresses a subject that is being increasingly used in the debate over Scotland in the Union and argues for a new approach to Britain’s constitutional question.

Prof Gallagher was Whitehall’s most senior civil servant concerned with devolution, working as the Director-General for Devolution in the Cabinet Office, the No 10 Policy Unit and Ministry of Justice.

He retired in June 2010 and is now an academic heavily involved in the Scottish constitutional question and a director in the commercial and charitable sectors.

In 2005, he was appointed Visiting Professor of Government at Glasgow University and has also been a Visiting Professor in the Centre for Public and Corporate Ethics at Glasgow Caledonian University.

Since 2010, he has been a research fellow at Nuffield College in Oxford. He is co-author of England and the Union, How and Why to Answer the West Lothian Question and of Scotland’s Choices, the Referendum and What Happens Afterwards.

Today's world is suddenly all about nationalisms, some of them very disagreeable, as in Hungary or the US, others very disruptive, like Brexit or, potentially, Scottish nationalism. This poses a problem for many on the left who think politics isn't about achieving national sovereignty, but promoting social justice. They struggle to deal with it, and find a coherent vision of how to reconcile people's need for identity and the demands of economic opportunity and social justice.

Brexit has upset the UK’s constitutional applecart, and this English nationalist project has encouraged Scottish nationalism. Both projects seek to break up multinational unions in the name of sovereignty. Brexit has already split the UK down the middle, and similar vote in some future Scottish referendum would create a fissure in Scottish society that would last generations. We need something better.

Whatever happens with Brexit, there is an alternative for the UK. The risks to economic opportunity and social justice presented by independence stem not from acknowledging Scottish identity, nor from increasing Scottish autonomy, but from breaking the economic and social bonds of the United Kingdom. Its domestic market is vital for Scotland's economy, and sharing resources across the UK supports social justice in Scotland through welfare and public spending programmes, as we saw again last week the latest GERS figures.

We do not have to lose these benefits in order to gain more autonomy. Instead, Scotland, and the rest of the UK, should move to a more federal system. The structures of federalism, which means different levels of government each with their own responsibilities, can support different social models, but I argue for a progressive form of federalism, one designed to create the maximum scope for social justice in each part of the country. Here is what it would mean for Scotland.

First of all, it implies a change of mindset in the whole UK, from the worn-out notions of parliamentary sovereignty which drive so much of our overcentralised government, especially in England, to an understanding that the UK really is a multinational state, a voluntary association of nations which come together to preserve their identities and promote their shared interests. That implies a better form of entrenchment for devolution in the UK constitution. Given the circumstances of Brexit, it means entrenching wider powers too.

More important, perhaps, it implies a design which embeds the purpose of social justice in the territorial constitution. The federal UK parliament and government should be responsible for providing a guaranteed level of welfare and public service provision across the whole territory, irrespective of whether local taxable resources are big enough to support it, much as today.

But government in the devolved nations should have the capacity to increase this from their own resources if they think it necessary. That’s an each-way bet for social justice.

We’re already close to that for Scotland today. Not only is the Scottish Parliament responsible for most major public services, but it can supplement any welfare benefit it thinks unjustly small. It has the money too: not only is the devolved budget about 25 per cent per head higher than English levels, Holyrood has wide tax powers too.

A UK which followed these principles would make a similar offer to the different regions of England. Many of those who voted Leave in the European referendum were expressing a beef with London, not Brussels: that's where they need to take back control from.

Those obsessed with sovereignty and identity see nationalism as an end in itself. History tells us this is a dangerous road. But those who want to promote social justice and co-operation between different peoples cannot ignore the human need for acknowledgement of their identity. For them the right approach is a model of progressive federalism, empowering the UK’s nations and regions in a way which gives each level of government the power to promote a just society.

This will be one of the themes explored by the new Think Tank Our Scottish Future being launched with an address by former PM Gordon Brown in Edinburgh this week.