The following come to mind if you're wanting good historical visits with a 'technical' side to them.

1) Tower Bridge Guided Tours
2) The 'Churchill War Rooms', Whitehall (Part of the IWM)
3) From a railway point - the London Transport Museum has a series of 'behind-the-scenes' tours of parts of the Tube, including 'Down Street' which was the WWII headquarters for the 'Railway Executive'.

Details for these should come up on the web quite easily.

(To which you might add the RAF Museum at Bentley Priory - wartime HQ of Fighter Command [not the RAF Mus @ Hendon]).

Hope this helps.

T