If he's intending staying in the UK he might be better getting the filler changed as some garages don't like you using adaptors as some of them can damage the seals on the filler (apparently) and they don't always seal that well.
Autogas 2000 (as linked above) can supply fillers that will take the bayonet style pumps without an adaptor although it will depend on the age and type of the installation how much of a job that will be. In fact as you're not a million miles away it might be worth taking the car to them and getting it sorted.
We used to have to use an adaptor on ours and it was a right PITA, so much easier with the "standardised" bayonet filler where you don't have to route about for an adaptor every time you fill up.
Autogas 2000 (as linked above) can supply fillers that will take the bayonet style pumps without an adaptor although it will depend on the age and type of the installation how much of a job that will be. In fact as you're not a million miles away it might be worth taking the car to them and getting it sorted.
We used to have to use an adaptor on ours and it was a right PITA, so much easier with the "standardised" bayonet filler where you don't have to route about for an adaptor every time you fill up.