I do have a feeling Bmth are one of headliners. Jack Saunders interviewed Oli recently so could easily have pre recorded a bit in there about headlining R&L to play tonight.
Could be a late-stage grab at relevance again. Wouldn’t headline on their own back, but being a secret set would make some buzz about them and they’re around. If I was a betting man.
Personally hope for much more interesting secret sets. A KOL or George Ezra type holds zero water for me.