Hi there just thought I would give you guys the heads up on this, having just put in a new fence after high winds, this stuff is great, far easier to use than mixing your own sand, gravel and cement also has the benefit of setting in around 5 min unlike concrete you mix yourself.
Dug my holes the day before and started the next day at 2pm finished by 5:30
8 concrete posts, 7 Gravel boards, 7 fence panels 3 1/2 hours.
You will need 2 bags per post hole, less if you use some broken bricks or simlar to make the postcrete go further
Also £5.58 at B&Q