Okay - I have been having a think about this. Certain ISP's in the UK have a preshield virus / hacking protection system installed on their side. I think that my ISP uses that system to filter info and data coming in. This is obviously beyond my control and I have no say in the matter and I have no idea what their rules and protocols are over network traffic, however if you are using certain ports for this system, those could in theory be red flagged and the connections refused. If that is the case, it would make sense for me, but leaves the question open as to why others would get intermittent issues.