Fibres (was supplied by BT as point to multipoint when I was in the know; likely superseded by later iP cloud technology) and a more recent satellite backup, for the BBC. Dual fibres to each site, diversely routed so that one fault doesn't take the site off air. Satellite backup - used in anger when Bilsdale caught fire. ITV/C4/C5 got their own backup cobbled together as a result of that.
Coding and multiplexing is at two diverse sites and they have satellite uplink facilities, too. Studio centres feed over BBC's own fibre connectivity to the two C&M centres and to other studio centres.
There may still be a few 'fibre' routes that use microwave links to carry the data in the BT network; probably very few left now for that specific use (if any).
Virgin I believe 'collect' the signals from BBC (and likely others) using their own fibres.
Analogue TV was sent from studios to transmitter chains - often via 'self provide' microwave link to save BT vision circuit costs.
Radio distribution is, of course, a different matter - even to the same transmitter sites.