People ride a prototype of a driverless vehicle as it is moves through a pedestrian area in Greenwich, east London, February 11, 2015. Britain has begun testing driverless cars in four cities, launching the first official trials ahead of a series of planned rule reviews to accommodate the new technology. (Photo by Suzanne Plunkett/Reuters)

Emergency services work at the scene of a bus accident on the Kingsway in central London February 2, 2015. A number 91 double-decker bus had its roof ripped off after hitting a tree, causing injury to passengers and passers-by, local media reported. (Photo by Peter Nicholls/Reuters)

A competitor gestures as he crawls beneath barbed wire during the Tough Guy event in Perton, central England February 1, 2015. The annual event to raise cash for charity challenges thousands of international competitors in a cross country run followed by an assault course consisting of obstacles including water, fire and tunnels. (Photo by Phil Noble/Reuters)

An animatronic polar bear visits the London Underground on January 23, 2015, to mark the launch of Fortitude, Sky Atlantic&Otilde's new drama starring Stanley Tucci, Michael Gambon and Christopher Ecclestone, which premieres on Thursday 29th January at 9pm. A team of 19 Hollywood prop specialists spent six weeks designing and building the realistic replica animal with six to eight people working on the costume at any one time, using over 60 different materials. (Photo by David Parry/PA Wire)

A swimmer competes during the UK Cold Water Swimming Championships at Tooting Bec Lido in south London January 24, 2015. (Photo by Luke MacGregor/Reuters)

A Sumatran Tiger looks at visiting children from it's enclosure during the ZSL London Zoo's annual stocktake of animals on January 5, 2015 in London, England. The zoo's annual stocktake requires keepers to check on the numbers of every one of the 800 different animal species, including every invertebrate, bird, fish, mammal, reptile, and amphibian. (Photo by Dan Kitwood/Getty Images)

The “Hoegh Osaka” ro-ro cargo ship, operated by Hoegh Autoliners AS, sits grounded on Bramble Bank in the Solent near Cowes, on the Isle of Wight, U.K., on Monday, January 5, 2015. The car transporter was deliberately grounded after developing a list, shortly after it left the Port of Southampton. (Photo by Simon Dawson/Bloomberg)

Amateur contestants (L-R) Phil Bailey, John Hindle and Eren Emir pose in telephone booths during the annual European Elvis Tribute Artist Contest and Convention in Birmingham, central England January 2, 2015. (Photo by Darren Staples/Reuters)