Yup, I noticed that! ;-)
Yup, that would makes sense. Also zoning is only required for properties over 150m^2 which rules out the majority I would expect.
That is for control of the whole zone though (i.e. provision of interlock), not the individual rooms...
Its ambiguous, I will give you that. Other sources suggest that TRVs are required. You may be right though... proper interlock, timer control, and fully pumped system may be enough.
Indeed. I have never heard of a requirement to replace TRVs with newer or better ones. (other than perhaps some of the mechanical hot water cylinder control valves that used to be used to arrest gravity circulation). So in answer to the specific question (assuming the words of the plumber were correctly interpreted and relayed), he is trying it on.