Aren't the fire control systems of Belfast completely mechanical?
In which case, anyone hacking them over the internet (or defending against such an attack) is a genius.
I understand that Scratchwood was chosen as the target to demonstrate the guns' range; of all the targets that are very close to the guns' maximum range, it was deemed the one most deserving of a few 6" shells. So the guns can't reach slough and targets in central London aren't impressive enough.