It looks like you're facing the Sudbury transmitter
BBC is transmitted at the lowest mux frequencies and the fact that you can't receive these channels points to an aerial/cabling or connector problem.
Because the aerials and outside cables are exposed to the elements 24x7 they will fail.
All channels come from Sudbury so if you can receive the other channels with no problem then something else is afoot.
Do you have a close neighbour and if so, are they receiving the BBC channels?
Did anything lead up to this situation?
Few round here use the terrestrial signal (mainly sky) - BBC has returned two days ago but is breaking up all the time