The arguement of 'dismount as you may fill up & ride off without pay' doesn't hold water.
How many times do you see a driver sitting in their car while a passenger fills up?
Should they be made to get out of their car?
Are they ready for a fast 'drive off'?
Most fuel stations have CCTV. In the time it takes to fill up they'll have you on camera, albeit with a helmet on, but 'drive offs' normally get caught by recording the reg. rather than the face of the driver (unless they are well known to the police).
At many supermarkets that also sell fuel you have to drive forward to the kiosk to pay.
From the Children's Legal Centre Website.
Petrol stations- the Home Office has recommended that no one under the age of 16 should be permitted to serve petrol, however, this is a recommendation and therefore not legally enforceable
yet Trading Standards website quote.
It is illegal to supply petrol to anyone under 16.
I have filled up twice, once on & once off the bike. I must admit it seemed easier on the bike.
I open the visor when filling up (stops it misting up) so fumes won't get trapped even if they weren't heavier than air as has already been mentioned.
If the garage/supermarket won't serve you fuel point out that you are willing to remove your helmet providing the sign says ALL head/face covering items (including burkas, hoodies etc.) and that the policy is ALWAYS enforced by ALL of that companies businesses. Until then it's discrimination (biking IS a religion to some )