‘I predict riots in the streets of Britain,’ Jilly Cooper wrote recently. ‘There is a great rage in the country and I can feel it prowling like an animal.’ And what will trigger complete social breakdown? ‘Building on green belt land will be the final straw.’

The green belt is planning’s gold standard. It places a green ring around our major cities, holding back sprawl and protecting the countryside. Over the past 50 years it has achieved totemic status, like the NHS or A-Levels. The green belt is beloved of environmentalists, Middle England – and best-selling novelists.

Last month, the Government made these people very angry when it published economist Kate Barker’s Review of Land Use Planning. In a previous review, Barker recommended the UK build an extra 140,000 houses a year. Now she wants the Government to rethink the whole green belt approach, encouraging cities to build out into the countryside.

Typical reactions to the Review have been extremely hostile. Journalists, pressure groups and former ministers lined up to denounce it as ‘Armageddon’, ‘devastating’ and ‘complete lunacy’.

So is this the end of the world as we know it? Or sensible reform of a policy shibboleth? What are the implications for planners and the public?

Land use planning is usually one of the least exciting areas of urban policy. Planners are supposed to sit in dusty offices, sorting out disputes about hedges. While planning can be dull, it is critically important. It is one of Government’s principal tools for balancing economic, social and environmental goals. And because people generally resist development, planning must also balance protection and progress.

Green belts are our best-known planning tool. Introduced in 1955, there are now 14 green belts covering around 13% of England (Wales and Scotland have their own policies). The biggest surround Greater London and big cities like Manchester and Birmingham.

The policy has had many successes. British cities lack the sprawling patterns of American ‘exurbs’. By encouraging people and businesses to cluster together, green belts have arguably helped to grow urban economies. Most tellingly, they are widely copied – even in the US, where ‘wild west’ planning regimes are now very rare.

Barker recognises the achievements of green belt policy. However, she points out that England now protects twice as much land as the OECD average. Around 13% of the country is designated as ‘developed’. But besides the green belt, another 31% is classified as Areas of Outstanding Natural Beauty, National Parks or similar.

Britain will need more land – the population is growing, as is the proportion of single person households. Richard Rogers’ model of high-density urban development only takes us so far. Surveys show the vast majority of Britons want to live in houses with gardens, and this quickly uses up our stock of brownfield land. Against this backdrop, Barker argues, it will be essential to revisit existing green belts, and allow cities to build out into the countryside.

Barker’s supporters make three telling points. First, public support for the green belt is based on misunderstandings. In a linked IPSOS/MORI poll, 60% of respondents believed green belts protected wildlife, and 46% thought they preserved areas of natural beauty. In fact, both are protected separately. Importantly, only 17% thought ‘land on the edge of cities’ was the most important to preserve against development.

Second, not building on the green belt may be counterproductive. In fast-growing cities like Oxford and Cambridge, development has increasingly leap-frogged into the countryside proper. The result is more commuting, congestion and pollution than relaxing restrictions might have achieved.

Third, constraining land supply raises its cost. Analysis by Paul Cheshire and Christian Hilber (commissioned by Barker) suggests the UK pays a substantial ‘regulatory tax’ on office space: rents in central Manchester are an astonishing 40% higher than central Manhattan. Of course, the wider benefits of containment may outweigh these economic costs. But their sheer size suggests change is needed.

Green belts are valuable. But we cannot preserve them intact forever. Housing shortages, particularly in the South East, have put nearly 1.5m people on waiting lists. The Government’s Growth Areas programme will help alleviate these problems – but ippr’s analysis suggests a further 200,000 homes are needed by 2016.

Similarly, Britain’s cities need room to grow. Since the mid 1990s, big British cities have been in recovery mode, with population, employment and output improving. Northern city leaders want to tempt working families into the inner ‘city edge’, while providing space for economic growth. Brownfield land must come first, but if necessary, cities should be able to push into the green belt. The approach needs to vary from place to place.

In practice, some green belt land is already built on. Local and regional planners have occasionally reviewed green belt boundaries, and over the past 20 years, universities, business parks and housing estates have eaten away at it.

This Spring’s Planning White Paper should push on with belt-loosening. This is not an easy sell. As one planning insider told me, change is ‘sensible in practice, but politically ludicrous.’

The Treasury is more enthusiastic than Communities Secretary Ruth Kelly, who recently cast doubt on the need for ‘substantial policy changes’. Surprisingly, the Conservative leadership also wants a green belt rethink. But most backbenchers will hate it. And both Opposition parties will probably oppose other Government proposals, notably the proposed Independent Planning Commission (which will rule on future airport expansions and nuclear power stations).

The main challenge is implementation. To avoid sprawl, local planners need to be strategic about green belt development. And many local authority teams lack the resources to do this, especially in smaller cities and towns. As things stand, there is a real risk that planners will get rolled over by private sector interests. The White Paper must also provide means to build up local capacity before changing the rules. And it should set very clear guidance.

Green belt reform need not be the end of the world. But delivering it the wrong way could do far more harm than good.