Agriculture in London is a rather small enterprise, with only 8.6% of the Greater London area being used for commercial farming, nearly all of which is close to Greater London's outer boundaries. There are a few city farms closer to the centre of the city and about 30,000 allotments. There are of farmland in the Greater London area. Nearly all of the farmland in the London area is a basis for the growing culture. Farmland in London is predominantly present in five boroughs: Bromley (of which an estimated 35% is farmland), Havering (estimated 44%), Hillingdon (estimated 23%), Enfield (estimate 22%) and Barnet (estimate 17%). The Lea Valley is a significant centre for salad crops. History Many areas which now form part of Greater London were formerly rural and agricultural outskirts and still bear names which indicate this past: Ealing Common, Lincoln's Inn Fields, Shepherd's Bush and Wormwood Scrubs, for example. In 1938, the Greater London area became the first region in Britain to use a green belt policy and introduced the Metropolitan Green Belt in order to combat urban sprawl. A 2005 agricultural census carried out by ADAS showed that 423 holdings were located in the London part of the metropolitan green belt, around 0.25% of the total number in Britain. The total land managed was 13,608 hectares, half of which was rented. Less than 10% of the land farmed was used for cultivation of organic materials, and the total contribution that farming made to the economy, excluding diversification activities, was less than £8 m. However, London's agricultural industry was shown to be much more reliant on activities pertaining to diversification, with just under a third of farm income attributed to it, exceeding the national average. The report stated that whilst farming was not a significant part of London's economy, it did have a vital role to play. The report showed that farming was mainly concentrated in northeast London, but only included figures on arable farming (the surrounding regions of East and South East are where cereal farming is most prevalent). The report commented that livestock farming had decreased in recent years due to a lack of infrastructure (poor access to abattoirs and markets) and problems associated with being located close to the urban fringe (such as dogs). The report concluded that the low levels of stock in relation to permanent pasture suggested equine usage, something often related to diversification