Have you tried running something like the tracert command via a DOS command window or maybe a Visual Ping trace. You can usually find a free 30 day trial version of the latter.
Open a Command (CMD) window and run tracert 84.20.192.65 from the prompt.
Betfair can block requests like this but it should help you notice if there is a slow hop on the route. If you get blocked then change the IP to 78.40.36.27 and that should go through. I get nothing above 24ms on any of the hops so if you find a blockage then get onto Virgin Support and tell the Goon you need level 2 support in the UK...or else
I also use Virgin and many times I had so much latency it was unusable. The problem with their support is that you always get the goons first up..."turn off at the wall, unplug the cable"...etc.
I have found on many occasions that certain parts of the network get routed a certain way. I have proven many times to Virgin that they have a problem on their network but they have an escalation procedure(used to anyway) so unless enough people complain they will do nothing about it. If you get to Level 2 support you may find someone who can help you. It would certainly help your cause if you could find the offending IP address on the route. On many occasions it was a case of them eliminating the faulty link on the route and then it all speeds up.
Unfortunately most internet users aren't bothered by latency whereas we know it can make or break our day.
I hope that helps??
JG