Hi Britboy

Welcome to the Forum.

A lot of good advise here already. As to the pack my brother-in-law is ex Army Staffordshire Regiment, all his kit now is Berghaus. Swears by it or is that he swears at it <img src="/images/graemlins/grin.gif" alt="" />.
I don't camp or hike as much as I used too but when I did the old adage runs true " Buy the best you can afford" quality lasts, my pack is LOWE and is a med to large, additional pockets give volume and versatility. I've had it 10 years now and it's still going strong.
Not sure which corner of the UK your from but I shopped around the four in my town and tried them all, go with what feels right when it's on (and loaded if you can). Nothing worse than hiking with gear that rubs and pokes in you, takes the fun out it.