Thanks dawnsh for your comments. The Kensal Green Cemetery link has proved very useful and from that list paricularly the charges for reclaimed graves 6' 6" x 2' 6" or 7' x 3'. That would therefore be for older graves and so is relevant. My 7' x 3' seems about right. T
There was a lot of thinking and calculations that went into the size and depth of grave plots (some up to 15 ft deep). In part this was to produce a profit for the shareholders but also to ensure there was enough room for the deceased population to be buried. Mortality rates were taken into consideration as was the water table and many other considerations.
Around 1856 the London Burial Board drastically reduced the number of grave spaces when they laid down grave plot size as 9ft x 4ft and the charge was put up to 5 guineas (£5. 5s .0p.) from 7.5 ft x 3ft costing £3. 15s. 0d.
Cemetery Boards also liked to fill the space between first class plots with "pauper" plots as these were not allowed to have marker stones above them, this gave the effect of a more open cemetery rather than a crowded one.
One interesting book on the subject is This Garden of Death (History of the York Cemetery) by Hugh Murray (ISBN 0 9517737 0 4) if it is still available (I have had my copy for possibly 10 or 15 years.)
Cheers
Guy