“ever since that time of unbound paranoia the one unbreakable law of the British secret services has been: Thou shalt not snoop on Number Ten. Because we are not in the business of generating policy—it’s not a task for which agencies like ours are suited, and in those countries where spooks set policy, it always ends in tears. We vet politicians on the way up—that’s an entirely different matter—but by the time they’re moving into Number Ten they should already be above suspicion; if they aren’t, we haven’t been doing our job properly. And”