ICH60
Western Thunderer
There is a small selection of town maps, scale 1/500. At the moment they are only of the GWR area on the National Library of Scotland (link below) They show mainly the mixed gauge track plans around the 1886's of the towns covered. Swindon is obviously for a GWR man very interesting.
Ordnance Survey Town Plans of England and Wales, 1840s-1890s - National Library of Scotland
Ordnance Survey Town Plans of England and Wales, 1840s-1890s - National Library of Scotland