The law is an ass
Just found this which is a new one on me!!!
Portable petrol containers
The Conditions of Petroleum Licence allows petrol to be dispensed into a single demountable petrol tank, not exceeding 27 litres, for use on a motor boat or similar vessel, or into a portable metal container not exceeding 23 litres or into portable (approved) plastic containers not exceeding 5 litres. Portable containers must be:
o suitable for the purpose of storing petrol;
o suitably labelled to identify the highly flammable nature of the contents;
o constructed and maintained so that they are reasonably secure against breakage and leakage (of petrol and vapour); and
o fitted with a secure closure, ie a screw cap