The BBC say that the TV and Freeviewservices will be restored fully today. It appears that the power supply failed whilst engineers were going 'ground works' on the transmitter.
This is a very unusal event. The contractors, Arqiva, are a very professional outfit. They should be, they used to be BBC Engineering!
There is now a low power service, and today the full service will be restored.
UPDATE: Services were restored at 1541 (radio at 1439).
Also, the BBC have confirmed that an annoucement about the work was made on BBC North West at 1035pm on Tuesday night, but was not intended to cover the failure. This work was not posted on the BBC engineering page until the failure occurred.