This web site is good and can only get better (as they scan more 25 inch maps)
http://maps.nls.uk/
Select
1. Series Maps
2. In the north you'll need to select Ordnance Survey, Six-Inch, England and Wales - 1842-1952, in the south Ordnance Survey, 25 inch, England and Wales (in process) - 1841-1952
They seem to be slowly working north
3. Then select - "As individual sheets using a zoomable map of England and Wales"
4. Zoom in until you can clearly see the map squares - click on the area you are interested in
5. look on the right and choose the map year from the one's available
The 6 inch maps aren't bad but the 25 inch maps are very detailed.
Ian