David WE Roberts wrote:
I need to dig and fill holes for 12 concrete fence posts - slotted
ones to take fence panels.

General guidance is they should be 2' deep.
Homebase 'how to' brochure suggests 1' * 1' by 2' hole for a 4" post.
This seems generally O.K. apart from the issue that if the concrete
post is on the boundary then the concrete filling will go 4" into the
neighbouring garden. Please tell me if I am barking up the wrong tree.

Whoa there!

Far too complicated. 12 posts, do yourself a big favour & invest £20 in one
of these http://www.wickes.co.uk/Post-Hole-Digger/invt/501584 sell it on
FleaBay afterwards or hire it out to neighbours.

Nice neat round hole about 8" diameter x however deep - I'd agree on 2'.

I bag of Postcrete/Postfix per post generally, if the hole goes a bit bigger
due to lumps of rock, roots then 1.5 bags per post.

Couple of tips. Never assume fence panels are actually 1.8m wide - they
vary +/- as much as 3/4". Concrete fence posts are 'kin heavy, get them in
the right place first time - you need a helper.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk