the north eastern railway's 2-2-4T "aerolite" which was used to haul the mechanical engineer's saloon before being preserved at the national railway museum

the national railway museum has lots of cool stuff. here's a tiny baby locomotive called "pet" which was used on the london and northwestern railway's narrow gauge railway at their locomotive works at crewe

oh entry to the NRM is free btw!

similar locomotive, the lancashire and yorkshire railway's "wren" for their narrow gauge works railway at horwich

these pretty tiny relatively locomotives - the terrier class - ran all the london southern commuter lines owned by the london brighton and south coast railway in the 1870s and 80s

on the other hand the great western railway was originally built to broad gauge - 7'1/4" compared to standard 4'8.5" - and the replica locomotives (here's the iron duke) are BIG

here's another broad gauge locomotive - a 4-2-4T with 9ft wheels used by the bristol and exeter railway

this is "hurricane" which was one of a set of v dodgy locomotives built to try and satisfy brunel's near impossible demands for the first engines for the great western railway https://m.facebook.com/DidcotRailwayCentre/photos/a.210517012308528/2426203314073209/?type=3&source=57

hard to imagine it ever worked well because it has such low adhesive weight

http://www.douglas-self.com/MUSEUM/LOCOLOCO/locoloco.htm is a great site if you're interested in unusual steam locomotives btw. there's a general unusual technology section too http://www.douglas-self.com/MUSEUM/museum.htm