An aircraft is not a 'public place', therefore the operators are within their (UK Law) right to prohibit photography
That may be the case but I know of at least one operator who has decided that these days trying to enforce any such "ban" is going to cause more trouble than it's worth. It has even told it's crews they must assume there will be cameras running if something " interesting " happens.
Astra
Any idea if the 350 "RAAS" is the same as installed in some Boeings? If (big if) it uses the same or similar logic there should have been a couple of aural prompts before spooling them up.