To Shambles et al
Musicians are no longer powerless.
In this case their 'freedom of expression' is being prevented for no good reason: no safety risk - no noise complaints.
Under the Human Rights Act, because they are directly affected by the local authority enforcement they could bring a case against the council. Remember: where there are two possible interpretations of the law, one that is compatible with European Convention rights, and one that is not - the compatible interpretation must be adopted.
In other words, counting members of the public as performers where they sing or play an instrument is the incompatible interpretation.
It's worth investigating.
H