I think this thread will continue until we have a definitive answer on this. My feelings are that the PRS is a self appointed collector of royalties not an official public body. The way I understand it (no doubt someone will have a different view or correct me if I am wrong) is that any act of parliament is only confirmed after it has been tested in court. I am not quite sure of the full meaning of 'common law' but I think that has something to do with it.
Anyway, my point is that unless someone has been taken to court by the PRS under the Copyright, Designs and Patents Act, 1988, that will be the only way we will ever find out how much power they have. It will get even more complicated when you take into account the fact that all garages and premises are different in design and layout etc as well as the number of employees and workstations. If the PRS had any real power we would have seen a deluge of business' taken to court for not having a licence. I have so far not heard of any but would welcome comments from anyone that has. This is a copy of the e mail that I sent them and to which I have not had a response apart from a further copy of the same letter.

Dear sir
I am writing to inform you that I am a sole trader and although I play music in my workshop no customers or members of the public have access and I have clear signs indicating this. Customers do have access to my office/reception but no music of any kind is played here.
Furthermore, in your letter you have quoted the Copyright, Designs and Patents Act 1988 (the act). Section 72 of 'the act' clearly states, that playing a broadcast to an audience that have not paid for entry or where the cost of the goods or services are not substantially attributable to the cost of the broadcast, does not infringe any copyright.
I will assume that you will not contact me again with regard to this matter.

Regards to all, Bryan.