Well I've been having the same issues since the swap over from adsl24 to coms.
Just seems that at random times of the day sites like, google, ebay, ebuyer amazon and my own
www.computerjohn.net cease to work but then magically come back to life hours later.
Its becoming a real pain in the backside. This move to coms has been a total downgrade overall. I was on the ADSL office 90 tariff and was connected at 19.8 Mbps down and 1.2 Mbps up. I've now been cut down to 16mbps down and 0.4mbps up.
I'm going to switch over to Xilo as they offer the 30day contracts and good service like adsl24 used to.