Well thanks everyone, I dampened the membrane which was very dry and rubbery, and loosened it from the chicks feathers because it had stuck fast, (he had made little or no progress) but did not break any more of the shell, he was then nearly half out and within a short time had come out completely. Time will tell now but he had obviously absorbed all the yolk and there was no blood so I think he was ready for help.
Thanks again, gosh it's a rollercoaster this hatching malarkey, and what time wasters, Mrs broody is getting a bit fed up with me I think.