Howard,
You say you have no terrestrial signal worth a damn.
Neither did I until about 6 months ago when my friendly local aerial shop suggested I change the aerial to a more modern type with some sort of booster.
I have no idea what he meant by more modern aerial but I gave it a go and now I have very good TV reception everywhere through the aerial.
I'm keeping Sky for the F1 and a few other things but my Terrestrial signal is now very good with the new aerial.