You don't need nonesense such as no drums or a ban on amplification. All you need is a simple statement of X decibels must not be exceeded between the hours of A and B. You get to set A, B and X. These may different for different times of day and for different venues. A pub in the middle of nowhere wouldn't need a limit on A, B or X as they couldn't possibly disturb anyone whereas a pub in a sidestreet of a housing estate may be treated more strictly.

"All you need is a simple statement of X decibels must not be exceeded between the hours of A and B."
How do you set this without some sort of licence?.

"Unamplified music does not need a licence and may continue in the absence of complaints". Simple and straightforward.

We tend to forget - this nonsense does NOT apply north of the border with Scotland. There, unless it is the main business of the place, music can take place. Good enough for Scotland apparently but not for England.