Andrew Carter is the Acting Chief Executive of Centre for Cities.

It is clear that the UK’s housing crisis has all parties in a bind. There are constant proclamations that the nation urgently needs more homes, but despite various proposals from across the political divide, there remains scant practical detail about where they will be built, and even how this would be decided. This is largely because each of the main parties have focused a disproportionate amount of attention on declaring where housing supply will not be found or delivered – namely within the green belt.

It is hard to think of another simple phrase that sends politicians ducking so swiftly for cover, clambering over themselves to ring-fence it and ensure that there is absolutely no doubt of their intention to ensure its unequivocal protection. The green belt has been exalted as sacrosanct in a way in which almost no other policy area has been indulged, and any attempts to have a serious conversation about its development have been swiftly stifled with the same kind of force as would usually be reserved for suggestions to entirely dismantle the NHS.

Politicians feel they have a political imperative to defend the green belt, and to promote locally-supported garden cities instead. But neither of these approaches reflect good policy – nor make good economic sense.

There is no single solution to building more houses, but at the heart of any response needs to be a focus on increasing land supply. And, with our housing crisis threatening the growth of some of our most successful cities – whose performance is vital to sustaining our national economy – we simply cannot afford to have the most viable source of land supply in the nation off the table.

While the UK’s housing crisis doesn’t play out evenly across the country, it is most acutely felt in cities that are growing and performing well. These cities also happen to be home to some of the lowest rates of house-building: between 2008 and 2013 there were relatively more homes built in Barnsley, the second most affordable city in which to buy a house given local incomes, than in London or Oxford – the least affordable cities.

The impacts are widely felt, not just amongst residents who are being priced out of their labour markets, but also within their business communities, which are struggling to attract the right talent or experiencing lower consumer demand. With rising demand and a chronic under-supply of inner-city land and housing, drastic action must be taken to realign the scale and geography of demand.

Densifying cities through their brownfield land is a good start – but there is only scope for 425,000 homes within the 10 least affordable cities, and given that many of these are expensive to build and awkward to develop, it’s hardly a short-term solution. More could undoubtedly be done to encourage and support cities to work with their neighbouring authorities to identifying opportunities to develop at the full scale of their local economies – which is critical when one considers that around 50 per cent of urban workers live and work in different authorities.

Making use of existing brownfield land, and encouraging more collaboration between councils are both necessary steps to ensuring we do not face this kind of crisis again in the longer-term. And yet, to get anywhere close to the homes needed to support long term economic growth, the reality is that local and national leaders are going to have to reassess the designation of certain green belt sites.

The first thing to note is that much of the green belt is far from green and, after doubling since the 1970s, it now covers 13 per cent of land – compared to the 2.3 per cent of land that homes do. Not all of this is the rolling green rural pastures that are so frequently conjured in public debate. The second, and most important point, is that only a fraction of green belt land would need to be developed to deliver the homes we need, where we need them – meaning the parks, gardens and sporting fields so important to communities, and to England’s natural beauty, would be retained for future generations to enjoy.

In fact, Centre for Cities’ analysis shows that building on just 5.2 per cent of green belt land within and around our least affordable cities would deliver 1.4 million new homes – all built at suburban densities and within walking distance of train stations.

In light of this, any business or individual feeling constrained as a result of the current housing crisis has every right to feel short-changed by the political debate around the green belt, and by the ongoing inertia afflicting all parties, which is preventing decisive action being taken. It’s time for leadership, and for parties to start bridging the gap between rhetoric and reality on the nation’s chronic under-supply of housing. It’s time for a sensible conversation about the green belt.