Significant Wall Cracking

If the blockwork was ok prior to the reno I'd doubt the new plaster is affecting the block. Generally if you have an issue with blockwork it will crack along the joints of the mortar, rarely right through a masonry unit. The long vertical cracks don't follow that logic. For the blockwork itself to deteriorate, without there being an issue with the block itself, the plasterer would have had to use some material that is corrosive to concrete or that type of concrete block which is unlikely.

You may want to get an engineer to do some investigation if you are worried structurally. If it was a foundation issue there would be some corresponding damage on the internal face of the wall as well. IMO it looks like the plaster coat might be de-bonding from the wall, this would lead to water penetrating and over time getting into the gap between the plaster coat and the blockwork behind. Freeze thaw in the winter would cause it to worsen over time. If you tap the plaster in that area does it sound hollow behind?

The plaster is fcked anyway so it might be an idea to take a portion off to see what's behind it. The bad corner in the first photo. If it is a de-bonding issue that's local to that area but with the potential to keep spreading you might be able to stop the rot with some quick action.

How man settles his debts is, frankly, none of you buisness.....! ;-)

What county are you in?

Asking as you may be in one affected by Mica or Pyrite.

Mica / pyrite did cross my mind, but in relation to the original structure. If you search how long it takes mica to show it says 6/7 years generally so it would be strange that it didn't appear before or apparent during your renovation considering your house is over 30 years old now. I've just read pyrite can show later (up to 30 years later) and I think that's more common in the Limerick area. Looking at the following link, some of the pictures of external render cracking look similar to yours. I think it would be worthwhile exposing a corner and checking the integrity of the blocks behind. If the blocks are fine digging down to the footing to expose and check that concrete would also be worthwhile.

https://www.draconsulting.ie/2019/09/hello-world-3/

There's a number of reasons it may de-bond, incorrect plaster mix / ratios used, not a good enough scratch coat applied or scratch coat not cured enough prior to top coat being applied among others. The infill of the cavity with pumped insulation can change how a wall performs and the dew point within a wall (where the condensation forms) which could lead to de-bonding also.

Fingers crossed it's de-bonding and not pyrite / mica. The lesser of the two evils. Best of luck with it.

PaidV.

I don’t understand why you have not included more photos of the adjacent wall in the middle photo (where there is a black downpipe). The Gully Trap of this downpipe is clearly seen on the top photo.

This wall is also shown severe cracking.

You should not remove any of the plaster from this wall, and do not interfere in any way with the cracks

It appears to me that the corner of the wall is subsiding, and may need to be underpinned with piles. This could be caused by a leak in the adjacent drains or could be caused by a leaking water pipe or some other cause. If that is the case then you may have a claim under your house insurance policy.

You need to retain a Chartered Civil Engineer or Chartered Building Surveyor specialising in house building insurance claims.