I expect you've seen these links already? Sorry not to be more help.

Clark, J.G.D., "Neolithic Bows From Somerset, England, and the Prehistory of Archery in North-West Europe", Proc. Prehistoric Soc., xxix, December 1963, pp. 50-98.
from the list at
http://www.student.utwente.nl/~sagi/artikel/misc/bibliography.html

also stuff at
http://www.wessexarch.co.uk/projects/amesbury/tests/prehistoric_archery.html
http://mypage.bluewin.ch/bfontannaz/ats/engl-Intro.html
http://www.xs4all.nl/~marcelo/archery/library/books/badminton/index.html

A mesolithic bow was found in Rotten Bottom bog in Scotland.

I think Rhiannon has got it well covered but there are a few extra possible sources.

This page gives an extremely valuable contact
http://www.archaeology.co.uk/directory/viewsoc.asp?soc=67&cat=2
I don't know Mr Soar personally but have spoken to him and he's extremely knowledgeable. He contributes regularly to an archery magazine The Glade (http://www.theglade.co.uk/) and also used to contribute to a US magazine Instinctive Archer, now sadly out of print.

There's also the Society for the Preservation of Instinctive Archery, some info at:
http://www.sptradarch.org/SPTA%20primpage.html

And I can recommend the Longbow by Robert Hardy and The Grey Goose Wing by EG Heath. The latter is out of print but some libraries have a copy. Got a first edition meself and guard it with my life.

There is also the sport of field archery, see http://www.nfas.net/ , within which some members recreate and shoot historic bows including some found in Britain like the Meare Heath Bow (think it's British)

I've been out of archery for a few years but there are many people who will help you if you start with the above contacts.

Many thanks for all the info and links - some interesting stuff there.

Alan