Much as I hate to get involved in this again, the actual phrase of Schedule 1, Part 2, Clause 11 states:

The provision of entertainment or entertainment facilities is not to be regarded as the provision of regulated entertainment for the purpose of this Act to the extent that it consists of the provision of (a) a performance of Morris dancing or any dancing of a similar nature or the performance of unamplified, live music as an integral part of such a performance, or (b) facilities for enabling persons to take part in entertainment of a description falling within paragraph (a).

Mumming is not mentioned I'm afraid, Peter. It is certainly not dancing so it is not 'dancing similar to morris'.

(As for my name, I've been DMCG on the Internet since I first used it decades ago, but feel free to call me Dave McGlade!)