Explosions can happen if flammable vapour from petrol is ignited, and the
presence of escaped fuel will always cause a fire to escalate. Fuel containers
must be made of appropriate materials to reduce the risk of leakage. The
container construction must conform to the requirements of the Petroleum Spirit
(Motor Vehicles, etc.) Regulations 1929 (S R & O 1929/952) or the Petroleum
Spirit (Plastic Containers) Regulations S.I. 1982 No. 630.

Petrol must be treated with the utmost care at all times, and that includes ensuring that it's properly stored in a container designed for holding petrol. When an examiner came to inspect the petrol tank on one boat he was visiting, he was horrified to find just a piece of electrical insulation tape covering a hole in a rusty and old outboard storage tank. Apart from leaking petrol each time the tank was moved, the hole also allowed dangerous vapours to escape, giving further opportunities for an explosion to occur. Don't wait for your rusty outboard tank to leak petrol before you consider replacing it, replace it now, it could prevent a fire. [5.4]

To avoid petrol leaking into the boat from fuel containers, they must be stowed
in accordance with Standards 7.2 through to 7.8, e.g. in a fire resistant drained
locker. This will allow fuel or fuel vapours to drain overboard, rather than into
the boat. [5.4]