I think YABU, which is not to say you aren’t allowed to be annoyed - but you have to think of the bigger picture.
We had a big extension done a few years ago, essentially doubling the size of our home. It was definitely unpleasant for neighbours - we discussed it with them extensively and were very sympathetic to their concerns. We also plied them with good meals, spa appointments, Christmas hampers etc. Fast forward a few years, it’s their turn to have their house done, and we have a year of disturbance ahead, so it’s swings and roundabouts. I have spent many hours advising them and helping with their project.
Meanwhile properties on our road are shooting up in value, because of homeowners like me who are investing in making the housing stock better.
As a neighbour, you benefit from the fact that the house next door has increased in value - it’s the halo effect.
The housing stock in England is very low quality, and not meeting modern life needs, so it’s no surprise that people want to improve it. Open living spaces, better insulation and windows, more storage and bathrooms, ventilation and energy efficient measures are needed in most homes. It’s part and parcel of home ownership - you have your parcel of land, and try to make the most of it. I’m afraid as a homeowner, you have to suck it up - there’s no point getting angry about it as it’s not within your control and your neighbours have a legitimate right to improve their home.