According to Yves Bréchet [1], former head of the French Atomic Energy Commission, the main difference is not regulation, government or public support. It's something that should speak a lot to the engineers on HN, but is almost always absent in public debates: the lack of technical expertise. Think expert welders, pipe-fitters, boiler makers, etc. The expertise required when making a nuclear power plant is very high, including and especially when it comes to welding, quality of steel, etc.
Costly mistakes were made while welding critical parts of Flamanville 3 for instance, requiring expansive and expensive rework. I don't think Hinkley Point C is faring much better. On the other side of the world China has been building nuclear power plants relentlessly: they have all the expertise needed. If you allow me a slight exaggeration, given France and UK massive de-industrialization over the last few decades, we are now amateurs compared to China.
Again, it's not an issue of regulation. It's just that when you don't build things the know-how gets lost very very quickly. Something that should get hammered in the head of all CEOs/managers/decision maker...
[1] https://www.thinkerview.com/france-la-strategie-du-canard-sa...