Thanks for the reply.
This is a purchased Cisco 837, not a BT supplied one. We don't use the 2Wire routers they provide at the sites. The current Firmware version is "12.4(5b)". I'm speaking generally. This is also advise from our allocated BT manager. However, the techies at BT themselves aren't sure to be honest, I'm going mainly on reports online off varying forums suggesting a firmware upgrade will work. However I don't have any particular versions suggested as an example unfortunately.
I do have the running config I can post if you like, however I've messed with the ATMO interface to destruction.
I do have a CCO contract, but I need to pay additionally for a firmware update, which to be honest, if I can obtain this for nothing for testing, I would rather at this stage. As if it works, I will upgrade the other varying Cisco's we have at the other sites to resolve the problem if and when it occures.