Ok, so some more info - last night we had an upgrade on our firewall, at that point it looks like a cable wasn't replaced properly and that eventually disconnected this pm. Our hosting company Rackspace (who were responsible for the work done overnight) then took approx 1hr 45 to diagnose and fix the problem (eg go to the firewall, notice the cable not in and push it in), which is obviously pretty unacceptable, but there we have it. Apologies again...