Do you really have a t1 in the UK? E1 is the standard in the UK. This gets really complex in that they must have a piece of equipment that take the t1 at your site and places inside a e1. At some point it will be taken out of the e1 and place back on a t1 as it enters the US.
There is little you can do. If you have a full t1 you just map all the channels to the interface on both ends and it should work just like a t1 in the US. You really have few options on a t1.
This type of error is almost always a issue with maping of channels between the e1 and t1 in the provider network.