From this morning, the BBC will trial various quality settings on its BBC HD service to determine what an acceptable quality level is for the broadcasts.
Whilst the changes are intended for the small terrestrial HD trial, it's not been made obvious whether it will affect those watching the broadcasts on Sky and cable services.
I'd be surprised if those services were also downgraded. Though the BBC is testing HD programming as a whole, the issue of broadcasting high definition programming reliably terrestrially would seem to be the main concern. I can't see much value in downgrading the quality of recordings for satellite and cable viewers. It's up to Sky and NTL to dictate how content is sent to its subscribers. The terrestrial trial, on the other hand, is in the hands of the BBC, and you'd expect them to be testing different technical aspects of the service.
Up until now the quality of the BBC HD broadcasts has been widely praised. The BBC HD team said “The tests will help us test the range of standards for optimum range and quality of potential future services.”
In any case, this set of trials will only last 5 days.
Via AV Zombie

Actually no its not in the hands of SKY how high a bitrate BBC uses its in thier hands since they lease thier transponders.
Cable on the other hand is cables choice.
Perhaps more research should have been done before blaming Sky for something they could possibly have no influence over. The BBC decide how they want to broadcast their FREE channels, nothing at all to do with any subscription.
The BBC broadcast Free To Air, no subscription at all!!! another bad mistake of the media thinking all things satellite are sky, they are not.
I just had a look at the terrestrial BBC-HD, it's broadcasting at 13Mb/s down from the 24 it was. I'm watching it on a computer monitor, and to be honest it doesn't really look any worse. Probably would on a decent set though.