sp00ks

IPv6 is enabled, but you were right that setting the MAC resolved the issue. Incase its useful, im using a laptop wirelessly that doesnt have an cabled connection. 

It did and does yes.

I can confirm by adding in my current credentials manually and get a 200 response. $Wcl=New-Object System.Net.WebClient $Creds=Get-Credential $Wcl.Proxy.Credentials=$Creds Invoke-WebRequest http://www.google.co.uk StatusCode : 200 StatusDescription : OK

Yes I can confirm the setup uses a PAC.