This has been floating around the internet for some time.
The funny part is that heritage zoning is the reason the addition looks the way it does. The upper floor was inaccessible and stairs needed to be added. Local regulations state that any additions must be visually distinct from the original structure so this monstrosity was the result.
Look up Caldwell Tower in Scotland for more information.
Here is the episode of The Restoration Man that documented the project - they go into the planning side of this in-depth because it's really a head-scratcher. The owner tried many times to get planning for more subtle alternations but they kept getting knocked back because it has to be distinctive enough that it's clear what is the old building and what are the new additions. What you see is the result of that messy process.
I'm going to go with the idea they didn't want anyone living in the tower in the first place. So they decided to refuse anything until it was too obvious to deny.
I work in stone conservation and for the body that dictates these regulations, even if it was built out of stone it would be required to be visually distinct. The only exception is if it were reinstatement of an original feature that had been demolished or decayed to the point that it had to be removed and fully rebuilt. In that case every effort should be made to source the stone from the same quarry, and the same mortar mix should be used.
An easy way to do that is make the addition not flush, or use a different kind if masonry. The linked documentary includes an interview with the local planning council who recommended finding a local architect with expirience to do it.
Instead the chrap English bastard just used the cheapest options he could find in Essex and wore the council down to approve this monstrosity.
Even if it went from grey stone to grey plastic siding, you could tell when it goes from stone to plastic. That should be enough to meet their "different" criteria, but not be such an outrageous eyesore.
Maybe, in case the next renovation is due, you know for sure which parts are to be preserved and which can be removed. However, some craftsman or architect doing that should be able to tell the difference between modern boards and windows and ancient ones without relying on the help of white plastics or baby blue paint.
However, if you own a cultural heritage building, the c.h. office has a lot of saying about each and every modification done, especially on the outside, so I doubt it's due to financial issues.
This mess is because the planning authorities rejected more subtle additions and insisted on something that is distinct from the original building, which is what they got.
Because though uPVC windows lack the myriad advantages of wood or stone frames, sometimes it is better for the ongoing fabric of a building to just get it weatherproof until someone comes along who can afford to put in more suitable replacements.
Then white uPVC frames are much cheaper than coloured versions.