"We need people to deploy into a range of situations around the world and people who have a different ethnicity can often go places and do things and meet people that those from a white background can't," he told the BBC.
"There are some places that white males can't go," added the official, identified only as Mark.
He downplayed the James Bond image, saying: "This is the biggest myth at the service -- we do not have a licence to kill -- we do not carry Berettas. That's simply not true."
"I think sometimes we're hindered by it -- because it gives people a false impression of what working for the organisation is actually like. It does tend to turn up quite a lot of thrill seekers and fantasists, and were not really interested in them," he added.