Is this any use to you? Use the slider to move between the old map and google earth, dropdown menu on the right allows you to change the modern overlay, dropdown on the left the old map, you can zoom in and out as well.
http://maps.nls.uk/geo/explore/#zoom=16 ... FFFFFFFFFF
There are more old maps with larger scales if you click on the "Find by place" select the series that you want on the left (25" to the mile has great detail), move the map around, then click on the point of interest, a list of maps should appear on the right, click on one and it will open in a new window.
http://maps.nls.uk/view/82891857#zoom=4 ... &layers=BT