The people under threat by the law are not musicians directly, but those publicans who allow you to play. They who can be fined for not havig a Public Entertainment Licence. So, if they think there's a likelihood some pillock is going to apply the law, they won't let you even if otherwise they'd like you to.
It's a stupid law, and the best way of getting them to change it is for prospective tourists to write to the papers and the politicians in England saying it is putting them off comig to England. So do it now - there's a debate about it next Wednesday, which makes this a very good time to do that.
I gather there are stupid laws like that in some parts of the States too. If there are, let's be hearing about them so we can write stroppy letters to your pillocks.