It's a busy weekday afternoon in East London. The sounds and smells of a nearby food market flood the street as businessmen dressed to the nines barge past me on their way to the closest tube station.
I slip through the crowds and make my way onto an innocuous side road, where an equally innocuous sign sticks out from a grey building and reads: 'The Altitude Centre'. You'd be forgiven for mistaking it for a travel agent, or walking past without a second thought, but here, among beeping taxis and jam-packed streets, lies a vital port of call for the endurance athletes and high-altitude mountaineers of Britain.
