Trivia: Longest distance between any two London terminals?

[USBT]

When Crossrail finally opens, some of these journeys will improve significantly. For example Paddington-St Pancras will become a one change journey via Farringdon.

Yeah and it will spoil a lot of these trivia threads too.

 

[itfcfan]

If you use German Railways (bahn.co.uk) as your route planner, you can see some interesting permutations it uses to get from between London terminals. It restricts itself to national rail services, although for a few routes it gives up and tells you to "Continue by public transport".