I remember hearing (possibly on the DVD commentary?) that the scene of Alan and Tony Hayers walking into the BBC restaurant was location, but the part when they were sat at the table was studio, with the set designed to match. On screen, it appears almost seamless.
Yes, although watching it now looking at it knowing that it is noticeable. Not only is the lighting and size of the room slightly different but the background atmos disappears soon after they enter the set.
Even though TV Centre did have a waiter service restaurant, pretty sure it wasn't filmed there, it doesn't look like it architecurally
The radio studio shots are not in a real radio station, I’d assumed they had just assembled a load of audio kit in a large room. All credit to the set builders !
Not a real radio station but a real studio - at UBC Media in London. Apparently Mid Morning Matters was filmed in the same studio
DeMarkay and Markymark gave kudos