Thanks for all your replies.
After some consideration, my thoughts where its £113 to win about £314(2.8 - 1).
I discounted him having a full house, because the raise all in makes no sense.
This leaves him with
a) he has a 5 - this means I have 10 or 11 outs (9 for the flush & 2 eights) - I may have deduct 1 out for his boat!
b) he has a flush draw - this means I must be ahead as I have the 8
c) he has a straight - this means I have 12 outs (9 for the flush & 2 eights & 1 five)
d) he has an over pair - this means I have 11 outs again (flush and 2 eights)
e) a complete bluff
at worst I should be 11/46, i.e. 3-1.
Allowing at least 10% for the flush draw, over pair or bluff I felt I had the odds to call and I called.
River Card was the

He claimed to have a straight ( 6 7) and folded when I showed the flush.