I can understand some the intentions:

Many buildings don't even have basic loft insulation. Especially (ex-) council houses.

Double glazing units should be fitted from the inside only, not easily removed from the outside.

I suspect a lot of this is down to enforcement. Their view must be that if you have the money to extend then you must have the money to bring the existing up to good standard. They will have the usual exclusions for listed buildings, etc., which brings us nicely to the Value Added Tax on repair versus new build scandal. Is that what you are referring to?

Having worked for central government, in buildings that didn't require local planning permission or building control, I am well aware of that issue. It just seemed like all the political types were fighting a jurisdiction turf war.