The london war museum was another place that was worth the time. It is in an inconvenient place away from town center, but has 5 floors of displays on multiple war periods, including recent wars, and even a section on the whole recent mess in Syria.
nice V2 rocket
human guided torpedo
They had a nice display about Mi6, the secret intelligence (as opposed to the MI5 james bond agents). Several of them infiltrated France during WWII and helped the French resistance to fight the germans: