There is a clear imperative for greater devolution within England. Highly centralised powers and budgets have failed to promote balanced regional prosperity beyond London and the south-east over recent decades. The disempowerment of provincial England contrasts ever more starkly with growing devolution to Scotland, Wales, Northern Ireland and London.

However, English devolution is highly problematic, not only in deciding what to devolve – do we want one NHS or 10? – but also to whom to devolve. And the realistic scale of devolution is not remotely on a par with the existing powers of the Scottish parliament and government, let alone the new tax-and-spend powers set to be devolved to Holyrood.

England has been a unitary state since the Tudors, long before the union with Scotland. Beyond London, there are few large regional units within England that command widespread loyalty. The debacle of the north-east regional assembly proposal, rejected by four to one in a referendum a decade ago, is a warning against creating artificial regions and expecting them to be regarded as superior to Whitehall and Westminster.

Equally, there is only limited scope for further devolution to England’s nearly 500 existing local authorities. Strategic responsibility for areas such as transport, skills, health and economic development requires greater scale.

The best first step forward is to devolve more to the larger cities and their travel-to-work areas, where there are ties of loyalty and consent. London is leading the way. The mayor and Greater London Authority, sitting above the 33 London boroughs, now have responsibility for transport, policing, strategic planning and economic development, alongside tax-raising powers.

Other city regions are starting to follow suit, and I strongly urged this course in my recent report on regional growth. The cities of Manchester, Leeds, Newcastle, Sheffield and Liverpool, with their travel-to-work conurbations, all now have “combined authorities” with strategic responsibility for transport and economic development. These five have been formed by the consent of their constituent metropolitan councils – and more powers, taxes and budgets (including business rates) should be devolved to them.

Together with London, these city regions account for a third of England’s population and half of its economic output. However, even within this group of cities, the “combined authorities” have only a fraction of the powers of the mayor of London. This is partly because they have nothing like the same level of democratic legitimacy, having no directly elected mayor or authority.

It is hard to see them becoming as relatively powerful as the London administration without an elected dimension. I support elected mayors for the city regions but most existing local-authority leaders are opposed.

Nonetheless, much of metropolitan England could not easily be incorporated into city regions by consent. Birmingham, England’s second city, is split between three local enterprise partnerships (Greater Birmingham and Solihull, the Black Country, and Coventry and Warwickshire) and there is no plan or common desire to move towards one. Even smaller cities such as Bristol and Hull, and their neighbouring authorities, are opposed to serious joint institutions.

More problematic still are the non-metropolitan counties, which often incorporate numerous travel-to-work areas and where regional identities of interest are generally weak. This is part of the reason why 39 local enterprise partnerships were set up in England after 2010 through a bottom-up process. A new process is needed to reduce these 39 substantially and to devolve responsibilities for transport and skills in particular to the new city and county regions. But achieving this by consent will not be easy and it may have to be a gradual process.

A bold, consistent and cross-party approach to devolution and new forms of civic engagement will be essential. They need to start now, as proposed by Ed Miliband in his call for a full constitutional convention engaging every nation and region.

None of this will create English regional units on a par with Scotland’s parliament and government. But nor is an English parliament an attractive way forward. England is so dominant within the UK that separate English and UK parliaments and governments are a recipe for weakness and instability. In any case, significantly different levels of devolution are going to persist between the constituent nations of the UK and within England even with extra devolution all round.

There is plenty of scope for improving parliamentary scrutiny of English legislation and administration by English MPs. But the UK must remain a partnership strong enough for the English to treat our neighbours with generosity, otherwise the union is in peril. Having just experienced the deep shock of a threatened separation, we English should be generous not mean-spirited.