Hi all
Thanks Henrik, Richard and Demon for the response with my problem, it is much appreciated.
It turns out Henrik spotted the problem and it is now sorted. Being lazy I copied and pasted a line for the interrupt enable from the handler line but didn't change from Handler to Enable as Henrik spotted. I then spent a week of evenings trying to find the problem, it is true sometimes you cannot see the wood for the trees.
Thanks again Geoff.