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The is a collaboration led by myself and Richard Blakeway, the deputy mayor for Housing, Land and Property at the GLA, working with members of HTA’s team and others. The study aims to identify how urban intensification of suburban London might contribute to an increase in housing supply, promote economic activity, improve local service provision, reduce congestion and improve the sustainability and quality of life in the outer Boroughs.

The London Housing Strategy acknowledges a shortfall between the present rate of supply (averaging 16,300 homes per year over the last 22 years), the theoretical maximum capacity identified by the Strategic Housing Land Availability Assessment (SHLAA) of 42,000 homes per year, and the requirement to meet demand of as much as 50,000 to 60,000 homes per year.

We intend the outcome of the study to be complementary to the wider plan to increase housebuilding across the capital. And we recognise that the capacity to increase supply identified in the recent SHLAA assessment already includes the contribution of all currently identified brownfield sites, infill sites, redeveloped local authority stock and possible urban extensions.

If just 10% of the semi detached stock of outer London was fully rather than under-occupied it could accommodate 100,000 more people than at present

The study recognises the shortfall in supply from these sources and turns its attention to the possibilities inherent in London’s very low density and often under occupied suburban districts to see how the shortfall may be reduced in the future. It takes a starting point that London’s huge suburban tract is of variable quality and seeks to identify areas where there is potential for enhanced value through intensification.

The facts are striking. According to The Centre for London, 75% of people in outer London boroughs (compared to 50% in inner London) oppose new housing development in their neighbourhoods. In Bexley, based on the 2011 Census data, 45% of the population inhabit the ubiquitous three bed semi. Sixty per cent of households comprise two persons or less, 80% are owner occupiers, 66% own cars, 24% own two or more cars. In one neighbourhood of Bexley which we examined as a pilot, we estimated that at present 38 households comprise 110 people including only 18 children, responsible for generating 304 tonnes of CO₂ per annum. This pilot demonstrated how a series of changes over time could increase the population to 222 people at the same time as reducing the CO₂ generation to zero – a dramatic transformation.

Whilst it’s clear that Nimby attitudes thrive in outer London, we seek to explore the extent to which self interest may overcome resistance to change. The figures support our contention that doubling the density of just 10% of the outer London boroughs creates the capacity for 20,000 new homes a year – the area covered is simply huge so the capacity is correspondingly great and should not be overlooked either by the local authorities concerned or by London’s city fathers, who seek to find solutions to its housing crisis.

We calculate (on the basis of the 2011 census data) that if just 10% of the semi detached stock of outer London was fully rather than under-occupied it could accommodate 100,000 more people than at present. If the owners of this 10% took up their full entitlement of permitted development rights this could contribute the equivalent of 6,000 homes a year to the housing supply of London. And redevelopment of just 10% of the existing stock of poor quality semis at double its current density of only 30 or so homes per hectare could increase supply by a staggering 20,000 new homes each year.

Ben Derbyshire is managing partner of HTA Design