Owning your own home

Other dumb things like filling wall cavities (30s housing) with spray insulation that then allows damp bridging, filling the roof void with spray on insulation that then prevents any form of maintenance, fitting external insulation that prevents brickwork from drying out.

Could be a dumb question, but does rendering over brick front and back in a victorian terraced create that problem? Or is it about how and what rendering is done?

i'd lay the blame more at feckless contractors who will sell you the product they have/can get cheaply rather than what's suitable for your property rather than at IB's feet

it shouldn't be up to a protest group to make sure that alleged professionals are doing things properly

All this stuff those Insulate Britain clowns pretend isn't a thing

What makes you think that? ("pretend isn't a thing" not "clowns")

filling the roof void with spray on insulation that then prevents any form of maintenance

My mother, who is doing up her Georgian boomer pile to sell and downsize, had this done.

The place is now unmortgageable for buyers, who only had a limited pool of mortgage providers that would lend on a property with two addresses.

New roof time...

The examples you use to my mind are an example of why there should be intervention in the construction industry to make it a well regulated, licensed profession. Not the current set up where it's easy to hide a lack of competence and knowledge with a brass neck while merrily ripping customers off selling inappropriate solutions and products.

There is no reason to not retrofit insulation into an old property. It will never be as effective as insulation in a modern property that has been designed from the outset to be well insulated but if it is specified and fitted correctly by people who know what they're doing it can drastically improve the energy performance of a building.