Well, not necessarily. A rogue commander could probably persuade his subordinates that he was authorized to use the bicycle key. If someone in a position of apparent authority claims that they will accept responsibility, subordinates will usually go along with that.
The WE.177 (http://en.wikipedia.org/wiki/WE.177 -- note corrected designation) was a free-fall H-bomb, carried on Vulcan and then Tornado bombers, and retired by 1998; you can see details of the 'bike lock' security on that wikipedia page. As such, it was stored on RAF bases and there are extensive procedures in place to ensure that a rogue officer can't order a deployment without it coming down the chain of command. (See also "Dr Strangelove".)
The WE.177 was not a sub-launched missile. The Royal Navy's Trident D5s (which come from the same maintenance pool as the US Navy's missiles) are; they do not, as far as I know, use bike locks: if they do, so do the USN's D5s.
