Short-sighted politicians
Our incompetent politicians chose short term electability over long term energy security and so let our home grown nuclear industry die out, and now they and everyone else are bemoaning what was done. My Dad worked for TNPG on Hinkley B back in the 70s and saw what was coming so transferred to a US nuclear power company, but even that faded away in the 90s. Too many NIMBYs wanted cheap reliable electricity but they all wanted it generated in someone else's backyard.
Then we had Chernobyl where a poorly built nuke in country that lacked reasonable safety precautions blew it's top (non-nuclear but effectively a big dirty bomb) and now everyone wanted nuclear power banned everywhere, regardless of whether it was well built, safe, and reliable or not. In Japan money grubbing cheapskates decided NOT to listen to the engineers who told them to put the emergency generators on the roof of the containment vessels, and that (helped by the Tsunami) gave us the Fukushima meltdown.
Because of the Calder Hall/Windscale fire in the UK we were one of the first to regulate the nuclear industry and rightly so, but that regulation has now turned into a monster that needs cutting down to size. So, here we are with nearly no nuclear power industry of our own and having to buy ours from the Americans, Chinese and French. We currently have 4 sites generating power, Hartlepool, Heysham (1 & 2), Torness and Sizewell B, but 3 of those will probably end power generation in the next 5 years, which leaves us with Sizewell B. France on the other hand has about the same population level as the UK, but has 56 (soon 57) nuclear reactors generating power versus the UKs 10.