There was until relatively recently a complete abandoned
Class 37 sitting on an out of use loop just west of
Nottingham station. It was railfreight oil and petrochemicals sector liveried and so can't have been there any longer than about 20 years. I haven't seen it for a few years though, think it just 'vanished' around 2006 time. Wonder who has it now...
There was also an
Intercity mk1 carriage just north of
Preston station that had sat in the middle of the tracks for quite some years until recently...
And east of
Edinburgh between Craigentinny and Newcraighall there's a whole bunch of stuff including a complete OHL electrification set left over from the ECML electrification program, several intercity and BR era carriages dotted around Craignetinny and a lot of other interesting stuff.
There are also some
Seacow wagons - early nineties vintage that have sat near
March station for quite some time.
There is also some sleeper stock (can't remember if it is intercity or CalSlep liveried just off one of the branches to the WCML - it might be Newcastle-Carlisle or Settle - Carlisle or somewhere else - can't quite remember!
And at
Doncaster (on the southern approach) there is also a very very old black BP tank wagon - it looks pre-war to me, possibly even 1920s! Rivetted pannel construction - very very antiquated.
Very interesting thread!