Indeed, it might be said that they underestimated the cost and timescales to get the project off the ground. But this is generally the case with mega-projects.
Guess we shall see how the construction of Sizewell C goes.
Their estimate was somewhat justifiable. Just recently before Hitachi finished it's ABWR in Japan for 3bn in under 4y... EDF thought they are cocky and can do the same...
Citation needed. Delayed since FiD? Or since the project was originally announced? To me the latter is rather an unfair given planning permission issues and government changes.