I don't think anyone should accept the idea that if something is pre-mediated that means it can't be spontaneous. (I know the word doesn't appear in the act, but it very likely will appear in guidelines and so forth.)

The primary meaning of "spontaneous" in the Concise Oxford Dictionary is: "Acting, done, occurring without external cause; voluntary, without external incitement, as made a spontaneous offer of his services.".

So if a publican, for example asks around, saying says "I'd like a bunch of people to come and play here on a Friday night" that'd mean the resulting session might not count as spontaneous. But if someone goes into a pub and asks the landlord "Would it be all right if me and some friends had a bit of a music session on a Friday night" and he said yes, I can't see how the resulting session would be anything other than spontaneous.

Yes there are all kinds of possibilities in between, and room for arguing about things such as "if someone buys you a drink is that payment", and I hope that we don't have to get into those arguments, but that there'll be a rational amendment in our favour. But it seems pretty self evident to me that the idea that something can't be spontaneous just because you planned to do it in advance is nonsense.