UK nuclear plant hit by new multiyear delay and could cost up to £35bn | Latest overrun to Hinkley Point C a blow to UK energy plans and French constructor EDF

It happens with almost every nuclear reactor built, no matter when

Brexit could be playing a big part too.
Worker and material shortage have been problems caused by Brexit in other industries too. Inflation is also blamed for the increased price, and that has been worse in UK after Brexit than comparable EU countries.