For point of reference, it would appear that many UK BT customers are having the same problem.

Having looked into settings and ip's it would appear to be hitting the BT ip 86.xx.xx.xx ranges, not the 81.xx.xx.xx sets.

Use this information to pass onto BT, if any consolidation it's happening to business connections too.

It is also just BT, not mIRC as everything works fine on my alternate connection @ home with main PC.