DavidR here are my responses...
Have you used avast before ?
If so what version and build, crucially did it work ?
Yep, been using it on several build for years. This computer has had it installed for about 2 or 3 years through several rebuilds. Not sure of the versions, but I do have all of my computers set to automatically update and I update all of them manually once a month just to be sure.
The behaviour shield has no impact on this problem, certainly not at a level of internet connection.
Do you use a proxy to connect to the internet ?
Nope, no proxy, just a DHCP assigned address from my Netgear router. I also have it set as the DNS and Gateway.
The win7 firewall has outbound protection disabled by default, so if you didn't enable it then it isn't or shouldn't be an issue.
By a fresh install, was this with a Retail copy of wun7 or a Recovery install back to factory install as this can come with a pre-installed AV ?
Full retail copy of Win 7 Professional. It's a custom built rig and I added a new SSD HD and moved the 500Gb to the D drive. Reformatted both drives as NTFS as part of the Windows install.