They could be cryptographically signed as the BBC Radio 4 LW carrier is phase modulated with a datastream that can be used for remotely controlling electrical equipment [0].

[0] https://en.wikipedia.org/wiki/Radio_teleswitch

You can't spoof Radio 4. There are too many tells. The news readers are rarely changed and you know their voices. Those voices are also very English and you can't take English schooling and BBC training overnight. Plus the airwaves. To take out 198 longwave and substitute something else is not so easy.

Except that the British succeeded in doing such spoofing in WWII.[1]

[1] https://en.wikipedia.org/wiki/Aspidistra_(transmitter)

That's talking about spoofing someone reading out numbers. You just need a German speaker for that.

The person you're replying to is talking about the impossibility of faking a day of idiomatic BBC Radio 4 broadcasting, and I'm inclined to agree that the individual personalities and programmes are so incredibly ingrained in most British minds and the details are so subtle that you'd have no chance of being convincing.

Sefton Delmer, who was behind that, went much further. Listen to this old BBC radio show about it. [1] Start at 30:55 for the intrusion operation. They did replace German radio stations in-place as they shut down due to air raid warnings.

[1] https://ia800108.us.archive.org/9/items/OperationAspidistra/...

I am sure deepfakes for radio is even easier to achieve than other media. Not only is it audio-only, but it is also low fidelity audio.