I mean you could 'tile' your wall with slimline double glazing panels and cover this over - similarly impractical but interesting such products exist.
I hadn't realised these boards all require plasterboard, something that could take a skim sounds preferable.
Interesting point on the regs, do you now where I can find that clause because I'd no idea. I mean, in practice it's probably a non-issue and if you hadn't told me I'd have proceeded blissfully unaware But it's good to know these things.
I don't know if I could get a modern reproduction of the coving, my guess would be yes but then removing the original stuff sounds a bigger job and I end up redecorating the entire room and potentially replacing the ceiling too?
However I kind of just don't WANT a modern version. Original features are nice to keep where possible and this isn't always the most practical option!
Part L (Approved documents) 5.7 Renovation of Thermal Elements (Page 19 half way down). And yes I spent many hours (and a certain amount of cash) preserving the existing coving in one house.