Dan Raven-Ellison is a "guerrilla explorer" who helped make London the world's first National Park City. Here are his picks for London's best green spaces, from wetlands to forests.

London, with its dominant skyscrapers and perpetually murky skies is often cast as a grey metropolis but nearly half of the UK capital is made up of green and blue spaces, including more than 3,000 parks, 400 miles of waterways and 8.4 million trees.

We spoke to London National Park City founder Dan Raven-Ellison to find London’s greenest spaces.

Daniel Raven-Ellison is a British geographer and “guerrilla explorer” who led the campaign to make London the world’s first National Park City. He is also a National Geographic Explorer and Ordnance Survey GetOutside Champion.

“People often think of London as this cultural, political and financial centre. It’s an incredible ecological centre too,” says Raven-Ellison, who is also a National Geographic Explorer. “London has nearly as many trees as people and 15,000 species of wildlife have been recorded including more peregrine falcons than in Yosemite National Park.”