This is the document relating to fuel stations own guidance...
Page 70 onwards deals with containers where they comment...
A limit of two containers is generally accepted as providing a reasonable
level of safety on the forecourt and also allows for compliance with the
majority of storage conditions applicable to petrol supplied to the general
public for their private/domestic use. This does not mean that greater
numbers of containers cannot be legally filled but it will be for you to decide
on the appropriate numbers based on a risk assessment and a review of
your hazardous area classification; as is required of you by the Dangerous
Substances & Explosive Atmospheres Regulations 2002 (DSEAR).