Brilliant Steve,
It certainly seems to me that as our customers are at our premises for the purpose of having their car repaired and not for the purposes of listening to the music (and no charge is made to do so) then there is no infringement. I wonder if there is a waiting room and the music is on in there that might be considered to be an infringement but that could be argued "that the prices are not substantially attributable to the facilities afforded" i.e. contrary to item 2.b.(i)
In the light of this I really don't think we need to have a licence. I think I will send them a letter and see what their reply is.
Shaun