'Great minds think alike' @duncombec - I was just about to post something exactly like what you've written! As a fun little exercise which replaces Underground stations with the names of places around Britain, I think this is great. Yes it's not 100% perfect but then again does it need to be completely free of every single error for people to get even just a little bit of enjoyment from it?A few posters here seem to have had a sense of humour by-pass...
Personally, I love the idea of there being a non-HS1 Kent-Essex rail link, even if Basildon wouldn't be my first choice! It's a very nice attempt to get the geography vaguely right in connection with a slightly doctored tube... sorry, Underground map.
As others have said, I would work on correcting the spelling of places as the next step, then see what other improvements you could make.
@Sprigibax - thanks for sharing this. I think it's really quite interesting and it straddles the line between 'diagram of British rail services' and 'drawing of the Tube map' very well.
-Peter
(P.S. @birchesgreen - your map looks great too. Definitely would've made my travels around Birmingham a while back a fair bit easier!)