In reply to a post by Oddball:

Plusnet support say there is no problem after turning my modem off overnight but the problem persists and I have tried two routers (including the Plusnet supplied router) and two PC's with the same results.

The site is hosted by Amazon Web Services (AWS) - the massive "cloud" hosting capability.

What you're probably seeing is the results of firewalls and load balancers that don't care about ICMP and so just drop it.

Yes that makes sense. I just did a 4 hour stream on the site and it was fine so obviously what you said. Thanks for putting me straight.