My experience with the Schengen visa (for my wife) was that we had to apply for a specific country, but once we had it we could enter any Schengen country (and in any order). For example I remember one year the visa was from the Czech Embassy but we entered Schengen in Geneva and there was no problem. However the CTA doesn't seem to be like that, which means I guess there must be passport checks between Ireland and the UK, or some other way of checking (plainclothes immigration officers roaming around?).
So in conclusion, I'd like to get back to the UK to visit my parents, but not to the extent of smuggling myself in - they'll have to wait for the prodigal son (joke). Anyway the compulsory 8 day quarantine in Jakarta on the way back (you get a wristband that beeps if you even try and leave your hotel room!) is enough to put me off travelling at the moment since I get claustrophobic. Perhaps in 2 months I'll look at it again if some of the restrictions are lifted.