I've never thought the Bachmann 10ft WB wagons masquerading as London Transport were very convincing when compared to the real thing (See the LT museum example pictured earlier in this thread). I believe a better and cheaper alternative lies in the Hornby 9ft WB wooden framed private owner wagons. The two on the left I bought several years ago at swapmeets and have just finally removed the lettering as I want to convert them to LT match wagons. It was a quick job with acetone (nail varnish remover), which will attack plastic, but of course these are protected by the original Hornby paint finish.
The wagon on the right is a white metal Wills Finecast track cleaning wagon - appropriately designed to use cigarette fliter tips wetted with cleaning fluid from above. I bought it at a swapmeet about 20 years ago and soon gave up on cleaning track with it, but had always been puzzled as to its prototype origins. Now I'm wondering if its related to their LT ballast wagon kit, but I havent seen one of those.
Incidentally, I dont think many of these small wagons went far in the post war years, all the regular engineering works I recall used the 50ft Flat/ballast F3xx series wagons, the RW rail wagons (like Robert Thompson is producing soon), or the HW4XX series hopper ballast wagons as Cambrian has said.