Drivers are being made aware of a little-known rule at Tesco petrol stations.

While filling up your vehicle with fuel should be fairly straightforward, those looking to fill up anything else should be wary of the obscure regulation.

There are strict rules in place by the national supermarket which have caught motorists out in the past.

It is not widely known but anyone looking to fill containers can only fill up a maximum of two, and they must not exceed 30 litres between them.

Customers filling up at Tesco have been warned.Customers filling up at Tesco have been warned. (Image: Google Maps)

A Tesco spokesman said: “Under the Petroleum Consolidation Regulations, we are required to have a policy in place to ensure the safe use of portable fuel containers at our petrol stations.

“Our policy is that only two portable containers (with a maximum combined capacity of 30 litres) may be filled on each visit by a customer.”

The supermarket’s website lists the rules in more detail, specifying exactly which containers are allowed.

Only authorised plastic or metal containers can be used and the maximum capacity for a plastic container is 10 litres while a metal container can take 20 litres.

Petrol containers should be marked or labelled with the words: “PETROL” and “HIGHLY FLAMMABLE”, a hazard warning sign and the capacity in litres.

Tesco also added that the containers should also have the manufacturer’s name and the date and month of manufacture.

“The maximum amount that can be legally stored by a private individual, without formally notifying the Petroleum Enforcement Authority is 30 litres,” said a spokesperson for the supermarket.