Is it actually a regulation?
there are regs re the storage of petroleum spirit.
People have been prosecuted for storing petrol at home in contravention of them.
Noteably the guy who was discovered with a 50gallon drum in his garage, during petrol shortages, after his neighbour smelt petrol fumes coming out of his toilet pan. The defendant had panicked after reading of the problems with storing petrol and had poured some away into the drains.
But having read the hse website the regs seem to have been relaxed a lot since I had to deal with them
Familiarity breeds contempt and its easy to forget the amount of potential energy stored within a gallon of petrol.