Martin Walshaw, consulting systems engineer for security at Cisco, says his passion for running, cycling and mountaineering is driven by two factors - the fact that, as an asthmatic, he shouldn't be doing any of them, and his fear of heights.

"It's a little ironic, I know. But it's in my nature that if someone tells me not to do something, I'm going to do it. I'm a strong believer in facing your fears," he says.