I did get it sorted and it was a blockage in the spray arms which ended up being fixed relatively easily. I managed to find out that the arm was removable and took it off. It rattled amazingly loudly.
As it turned out, the noises came from bits inside the arm which were pieces of glass and bits of broken "china" (or whatever cups, mugs etc. are made from these days!).
After removing those and replacing the arm, it has now run perfectly about 5 or 6 times.
Thanks to John for the tip about where the problem mght lie.
Jim Jackson
August 2009