The Unit Volume is cu meter.
There are a number of units: I thought the answer might be "cord" which is used, particularly in US and Canada, but it doesn't fit with Atwood's book "Cat's Eye". The answer must be "Stand" which is a further unit.
We had to laugh with the reference to the telegraph crossword. We struggled with this too, it is a stere. Doesn't come up if you google it but once you know what you're looking for you can find it!