It would have been a lot worse without "Cockcroft's Folly" - massive filters built on top of the "chimneys" that caught radioactive crud coming up the stack.

These reactors weren't build for nuclear power or anything, they were built to create the right kind of nuclear materials for weapons. They were essentially a couple of bloody great big nuclear bonfires!

He also along with Ernest Walton developed the Cockcroft-Walton multiplier, which is a clever arrangement of capacitors and diodes that produce a very high voltage from an AC source. Initially these were used in "atom smashing" cyclotrons, but came to be used in every CRT television you've ever seen.