Glenn I was having a look around and the consensus seems to be some people prefer using root hints and some people prefer using forwarders. In my opinion both options have their strengths and weaknesses. Forwarders rely on your ISP informing you that they are changing their DNS Servers and you may experience the unlikely event that both their DNS servers would go down. But then I always have the option to use root hints if dns servers are unavailable, so its redundant.

Root hints is slower than using forwarders and you also have the issue of some wierd windows bug or update causing issues - this has happened more than once.

As the primary problem with my network issue is to do with the actual Router, I will for the moment set the windows servers to forward to the ISP Dns Servers rather than forward to the BT Router. I am going to be getting rid of the router by connecting the linux firewall directly to the modem.