A Northern Powerhouse needs collaboration, vision and planning more than it needs cash.

During a brief visit to London, we called in to the New London Architecture exhibition at The Building Centre - it's just round the corner from the British Museum and well worth an hour of your time not least for the splendid model of central London at the heart of the exhibition. The NLA uses this magnificent visual to present a vision of the new London emerging through investment, initiative and development and is accompanied by a series of short films featuring NLA's urbane chairman, Peter Murray, talking through the challenges - homes, transport, place-making, environment - and setting out what's already happening and how built environment professionals including architects, masterplanners, designers, engineers and builders can deliver a better city.

What comes across in these films is the scale of engagement between public and private sectors - the projects highlighted on the grand model or featured on the wall around the space are mostly private sector projects. For sure there are the great transport schemes sponsored by London's government and supported by national governments but we also see investment in public realm, privately or in partnership with boroughs, by the great estates - Cadogan, Bedford, Grosvenor and the Crown - that enhance the City's character and variety.

Above all there is both a sense of vision - one shared by mayor, boroughs, transport chiefs and developers - and an intense granularity to that vision. We're so familiar with vision being just that - grand sweeping words accompanied with carefully touched up pictures. But this London vision comes with hundreds of individual projects, with emerging plans across the 32 boroughs (all pictured on the walls around the huge model), with examples of individual masterplans for smaller places and with specific project plans ranging from hospitals and university facilities through housing schemes to pocket parks or street markets.

While enjoying the scale, scope and ambition of this NLA exhibition, a profound depression fell on me. We ask about the North-South divide and tend to couch our understanding of this gap in historical terms as being about what was not what will be. Yet this model and exhibition, tucked away in a corner of central London, gives the lie to this convenient belief. The North-South divide - or rather the contrast between the dynamism of London and the sluggishness of Northern cities - isn't about some past event but is about the here and now, about what London is doing today. Worse still, what an hour with the NLA model told me, the divide is fast becoming a unbridgeable chasm - what London is planning far outstrips anywhere else in the UK.

London is sprinting away from the North. Not, as too many want to believe, because the city has been favoured by successive government or because the current occupants of Downing Street are stripping the North of 'resources'. The NLA films, the projects described, the masterplans - none of these even mentioned central government funding or support. Yet, as we saw recently in the IPPR North and Centre for Cities reports on the Northern Powerhouse, the starting point for the debate about growth in the North is to argue for more central government resources. But why, other than sympathy, should government simply hand over cash to one or other Northern city? Having Andy Burnham shout about a mythical "One Billion Pound Black Hole" is great campaigning - plays to the sense of abandonment felt in some places 'up north' but it's just the politics of the begging bowl, of holding out the flat cap while intoning the old mantra, "got a bit of spare change mate?"

Back in 2005 architect and urbanist Will Alsop was commissioned to look at the development of the M62 Corridor, that strip of England from Liverpool to Hull. Although the result was a typically Alsop mish-mash of ideas (and giant teddy bears) the premise was a good one - we could have a linear city 80 miles long from coast to coast. Let's remember it's 50 miles from Heathrow to Tilbury and the government has commissioned a Thames Estuary study to look at bringing North Kent and South Essex - from Canterbury and Southend - into London's planning purview. A connected 'city' from the Wirral to Bridlington isn't all that far-fetched.

Yet the current position - Transport for the North aside - is that the government, through its devolution programmes, is simply creating the basis for future competition and resentment. I was sat at a meeting recently where person after person started what they said with smilingly snarky comments about Manchester and how the Northern Powerhouse was, in truth a Manchester Powerhouse. This chimes with Mick McCann's brilliant essay asking why the BBC hates Leeds - a reminder that those Northern divisions are as much of a barrier to our progress as core features of our cultures.

Next year Manchester and Sheffield (or rather Greater Manchester and South Yorkshire) will elect a mayor, a new shining leader who will drive forward the future development of those cities. Other places will be waiting a while longer (probably until the little devils are skating on the ice in the case of West and North Yorkshire) but the message is that we will have a set of competing places across the North - Liverpool. Manchester, Leeds, Sheffield, Newcastle. And those mayors will fill the early morning London trains with their cohorts - off to that London where they'll make the case for central government to spend more resources in Liverpool, Manchester, Leeds, Sheffield or Newcastle. Not in The North - there won't be any sense of Northern Vision, no real Northern Powerhouse.

If we want a Northern Powerhouse, and I think we do, then it has to be pictured, planned, consulted on, organised and - so far as we can - funded from The North. And it's no good unless the whole resource - men and money - of England's North Country is brought to bear on that vision. We've seen this can be done for transport, we need to stretch that to the whole vision of a future economy.

A couple of days ago the Royal Institute of British Architects announced a new national centre for architecture in Liverpool. Great news for that city. Perhaps what we now need is a New Northern Architecture with the initiative and vision to build a model like the one I saw in Store Street yesterday - a model showing how private and public, local government, universities, manufacturers and housebuilders can share a detailed idea of how a future North of England will develop, will look and will work.

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