I don't much care what the MU says, it's not in the spirit of not meeting persons from other households indoors. Local rehearsal space owners seem to be of the same opinion. This quote from one of them makes perfect sense to me....
"We know a lot of our customers are professional musicians, but unless you are actually paid to come to rehearsal, then the announcement is very misleading. We cannot stay open for one or two bands as most people will be locking down. The financial support is there if we close - if we open, we have to survive on our own and we won't last long on three booked sessions a week. The rules are clear - no meeting of any other households indoors. This applies to us and we aren't prepared to risk an outbreak on our premises during lockdown. We also can't risk a £10,000 fine over what is a very grey area - different studios are reading and hearing what suits. We are, once again, being cautious and trying to remain safe as well as making sure we have a business to come back to."