Hillingdon and Hounslow are both among London's 10 greenest boroughs, according to a new map charting the capital's unspoilt land.

Nearly half of Hillingdon (49.2 per cent) is covered by open space, the fourth highest figure of 33 London boroughs, research by Greenspace Information for Greater London (GIGL) has revealed.

Hounslow is 39.6 per cent green, the statistics show, putting it eighth in the list of London's leafiest boroughs.

The figures take into account not just parks and other public open spaces, but also gardens, allotments and any other land which remains undeveloped.

The map, which shows Havering to be London's most verdant borough, was produced by GIGL to help campaigners make the case for a Greater London National Park.

More than 80 organisations are already backing the campaign, with high profile supporters including writer George Monbiot and TV naturalist Chris Packham.

Campaigners claim a Greater National Park would help conserve and enhance the capital's natural beauty, and ensure Londoners make the most of the greenery on their doorsteps.

In an open letter they today urged members of the public to become 'founders' of the park, which they say would not need planning powers to achieve its aims, by signing its petition.

"This is an opportunity to be part of a shared and transformative vision for London. From children to pensioners, teachers to gardeners, artists to architects and walkers to hotel owners, we can all take inspiration from a London National Park to make the capital even greater," the letter said.

"We are calling for the Mayor of London to complete a study into the opportunities, costs, benefits and options for making London the world’s first National Park City."

At 1,572sqkm, campaigners say Greater London would be the UK's seventh largest national park and would be home to 13,000 species of wildlife, living alongside the city's 8.3 million human inhabitants.

How green is your borough? (percentage of green space, according to GIGL)

Brent 21.9

Ealing 30.9

Hammersmith & Fulham 19.1

Harrow 34.6

Hillingdon 49.2

Hounslow 39.6

Kensington & Chelsea 15.1

City of Westminster 21.5