This year's exhibition of winning photos from the various categories has just started at the Royal Geographical Society on the corner of Exhibition Road and Kensigton Gore (a short stride from the Royal Albert Hall).
The postcode for the RGS / Exhibition is SW7 2AR and the nearest Underground station is South Kensington - about 10-15 minutes walk up Exhibition Road.
It's free entry and the standard of photography is (IMO) extremly good. If you're in the area between now and 17th August, it's worth the time to have a look around.