Hi Catherine
Congratulations on your new place.
I haven't totally read this thread, but if the TV aerial is an older one it will probably pick up radio better than a newer one because it won't have a `balun' in it. In my experience most newer TV aerials really don't do much for radio reception, whereas I remember years ago I could even DX Netherlands and France from an old group B X beam (though admittedly it was very very high up)
When you say `spare aerial sockets', so you mean a wall plate with more than one outlet? If that outlet is a FM / TV diplexer then yes, you will get some radio signal from it. If it's not a diplexer, you could replace the existing wall socket with one?
As for the aerial in the loft or outside, I've made an interesting (possibly to me only!) discovery lately. Antiference FM aerials don't have a folded dipole (which would be full wave for FM and quadruple wave for DAB) but they have two single dipoles spaced apart with plastic lugs. They call it the `trumatch' series. This means that the active part of the aerial (the dipole you make the connection to) is a half wave for FM, but also apx a full wave for DAB.
So an Antiference FM aerial (the 3 or 5 ele) works really well for both. Even on the horizontal plane it will pick it good DAB, but even better if vertically polarised if you don't need quite so much directivity.
I've currently got one of these up on the chimney vertically doing a grand job of FM and DAB. They're quite big but if you have a good open loft space it could be a possibility for you - then if you fancy a tinker for some DXing, you have some directivity too? Once you've moved in you might be able to figure some way of combining your loft radio signal with the TV one; you just need to work out where the distribution boards are (assuming you're moving to some sort of `block' of flats).
Of course reception conditions and requirements and different from one situation to another and you have to find the one which works for you. I think I've had just about every type of aerial on the roof before settling on this one, until I have my next mad professor idea......but seriously I think I'm done now as I'm happy with the result.
Once again hope you are happy in your new place.
Nick