//As an aside - NJ, for your 'tube challenge' did you have to step on the platform of each station for it to count?//
No. But the train must stop there. There are two stretches where one line serves all stops whilst another sails through. Between Acton Town and Hammersmith the District Line serves all stops and the Piccadilly Line runs non-stop. Between Finchley Road and Wembley Park the Jubilee Line serves all stations whilst the Metropolitan Line runs non-stop. At that time (though not now) the Metropolitan Line service pattern also included a non-stop service from Finchley Road to Moor Park (with some stopping at Harrow-on-the-Hill). That would not have done for the Tube Challenge either.
When I did the challenge there was no Piccadilly Line beyond Hounslow West (no extension to Heathrow), the Jubilee Line didn't exist (though the Bakerloo Line had two branches - one of which extended to Watford Junction), and the Victoria Line was still under construction. But Aldwych station was still open (rush hours only, which made the timing tricky), the Central Line extended to Ongar, the East London Line (New Cross to Shoreditch) was still part of the Underground - with Shoreditch also opening rush-hours only, the Northern City Line (Moorgate to Finsbury Park) was also still part of the Underground. There were 272 stations when I did the challenge - the same number as now.