Nerd puts it well. In the UK the PRS routinely sue premises for performing songs in public (usually by the use of records or broadcasts) without a PRS licence, and the principle is exacly the same as if the music were performed live.

In the UK the expression "derivative work" is not used with the same mantra-like pattern as in the USA but I think the UK law on adaptations comes to much the same as the US on derivative works. It leads to a big fuss sometimes when a perfomer thinks he is performing a traditional work, and the PRS says that a licence is needed to perform a copyright arrangement...