Not sure if anyone else out there is having as much trouble as me in sourcing the 'microfilter' for this, but after much hunting about i found a company that sells them: <a href="http://www.solwise.co.uk" target="_blank">Solwise</a>

They also have both internal and external ADSL modems as well as routers if thats your thing.

Just a heads up for any other UK users who didn't want to buy direct from BT..