I'm surprised this just came to light popularly, I've known about dead hand for some time, always scared the hell out of me- Mount Yamantaw is another point of interest, they're even related.
The British strategy is pretty good. Subs deep in the ocean, if they believe the UK has been destroyed, try to tune into Radio 4, the BBC news station. If they can't tune to it, the Captain goes to his personal safe and opens up a handwritten letter to him by the Prime Minister. He then bases his choice to launch or not by that letter.
http://en.wikipedia.org/wiki/BBC_Radio_4#History
http://en.wikipedia.org/wiki/Letters_of_last_resort