unless EH & NT are able to sort out the licensing situation.
But the problem is that it needs either a temporary licence each time at a handful of pounds but more importantly someone's time, effort and authority to push it through, or something similar to sort it at a national level, negotiating with each and every authority where a house happens to be ... I don't see it happening myself.

I suggest you get your contact to write to his MP and try to ask a question in the house. If he/she is a Labour MP, there's little hope of course. But if its another party something along these lines suggests itself.

"A member of my constituency has been informed that although he has sat in room at an English Heritage property playing period music for most weekends over X years, he will not be allowed to do so in future because of the licencing act of 2003. While this specific case is in the hands of English Heritage itself, will the Culture Secretary identify which of the main purposes of the Act -
(1) The prevention of crime and disorder;
(2) Public safety;
(3) The protection of children from harm;
(4) The prevention of public nuisance.

- made it necessary to bring such cases under the licencing remit at all?"