Thanks very much for the positive comments guys - much appreciated! I had thought I might have gone too far over the top with the weathering this time!
Dallas - the loco is standing on my little (2ft X 3ft) West Ghyll Adit layout. It was in the February 2005 Railway Modeller magazine but predated my joining this forum, so there isn't a thread. I could take some pics and post them though, if you'd be interested.
Wayde, the mechanism is the Bachmann HO 0-6-0 Plymouth switcher chassis with the centre axle taken out and some "side skirts" added to camouflage the fact that it started life as an 0-6-0.
Michael, the rust was depicted by painting the cab all over with burnt umber acrylic paint, then dabbing on rubber glue (Copydex in the UK) where I wanted the rust patches to be, then I painted it yellow, varying the tones by adding white to the basic yellow to lighten it in places while it was still wet. When the yellow was dry, I peeled away the Copydex, leaving brown patches, and then added more rust coloured paint to them and, while the brown paint was still wet, dabbed on rust coloured weathering powder to give some "body". I find two shades of rust coloured weathering powder are better than just one, to give the impression of varying stages of rusting.