Dagworth

That's how they made Radio 1 and Radio 3

Nahhhh...

There was first the Light Programme (sort of R2ish) and the Home Programme (R4ish), joined by the Third Programme (errr... R3ish).

Then in 1967 R1 materialised as the antidote to the Pirates, Light and Home metamorphosed into R2 and R4 respectively and The Third Programme clung to its designation (like the GWR after Grouping) and became R3.

Simples!