It’s good news that the regulations are becoming more onerous in England. However, in Scotland we have had minimum U-values for conservatories for some time
If you class the conservatory as an “unheated space” and don’t install any heating in it, then you don’t have to make thermal trade-off calculations with the rest of the house. What normally happens next is that the client gets everything signed off by building control, and then installs a radiator or electric heater in it – totally defeating the point of thermal efficiency. Of course, the best thing to do is to advise the client not to install conservatories at all – too hot in summer and freezing in winter. Better to install a sun room (in my opinion).