Everyone is entitled to their own view, but in the case of the current dire state of Swansea, caused by the aerodrome operator/owner, there currently is no ATZ.

Well that’s certainly interesting to know, but given there is still circuit traffic there I think I would personally treat it as active. Not much point having a midair just to be legally in the right.

I wonder if there is sometimes some confusion between an "active ATZ" (during published operating hours) and the zone being "active" - ie with flying activity - outside them. Cranfield's statement could well be interpreted as such. If so that is poor wording and would be better phrased as "flying activity outside published hours" or words to that effect.
Either way I'd have thought it foolish indeed to transit a known ATZ outside operating hours without making blind calls.

I think the best option is unless you have specific permission to enter an ATZ, either by radio, or in advance via email/voicemail....avoid it!

It's just too much mental work/hassle to figure out if you need permission of not, given the complexity of this issue.