I've tried taking readings at a couple of other places and I remembered when I had the engine cover off that I removed the hose going from the PCV to the inlet manifold while removing the vacuum pump. I thought I was going to have to remove the fuel line that goes to the high pressure pump that's attached to the vacuum pump. Anyway, on close inspection, the front of the PCV looked a little damp from oil. I replaced the PCV a couple of months ago and hadn't used the new pipes that came with it (not genuine) because the old ones looked good, as did the o-rings. So I replaced the PCV to inlet pipe and took it for a run. It felt like there was an improvement but I can't be sure, the pedal still gets hard, maybe not to the same point it did before though.