So i have managed to resolve my logging in issue. I was trying to resolve an issue with iWork taking an age to start and thought it to be perhaps a filtering issue. I found this not to be the case since another site was using the same proxy address and software with ni issues. I thought maybe firewall issue...

It turns out that it was neither.

I used my router's IP for the forwarding DNS server in the AD. Although the Internet was working and DNS working fine internally, it was causing issues with iWork not being able to resolve properly. Once the Forwarding DNS Server was corrected iWork worked fine.

Strangely though my login problem also disappeared. I'm not too sure why a forwarding DNS IP would cause problems with an internal logging lookup and client logging in but there you go. All seems Ok and pretty quick now again.

Thanks for your help everyone. Most appreciated.