When you license a song to play on BBC Radio it includes the clause that it can be used in any BBC broadcast, an old requirement from when BBC first branched into TV.

My understanding is that this comes down to "performing rights organisations" (PROs). They're the orgs that handle licensing music for stuff like this.

In the UK, we have only one, the PRS, and the BBC pay them a flat-rate fee - but this covers them as a broadcaster, not a producer. So instead of licencing the songs, they're paying a flat-rate to broadcast them (in the UK). This distinction is important because it even comes up when BBC licence shows to BBC Worldwide.

So if they licence the show to someone else who also has a flat-rate licence from PRS, then no problem. The problem is licencing it either to broadcasters who don't have a flat-rate licence (like Dave) so would have to pay a per-performance royalty, or to regions that aren't represented by the PRS (eg ASCAP, BMI and SESAC in the US).

So you get three options. One is to go through and ensure every single song used is represented by a PRO that you already have a flat-rate agreement with. Two is to pay per-performance royalties. Three is to replace it all with something royalty-free - performances you've commissioned, you own the rights to, or you can licence much cheaper.

Streaming further complicates this because you'd need to do the same for every region it's going to be available to. So armed with a licence from PRS and a licence from ASCAP, you're covered for .. two countries out of almost 200. These PROs can't licence you worldwide rights because they don't have worldwide rights to licence.