I completely agree that wearing uniform on a long haul is not something I would like to do however...
The idea of a security guard telling that the uniform may cause offence and that I should change does not wash, especially a G4S staff member. That company is a disgrace. The person in question should be fired for not being aware of company policy and bringing them into disrepute.
I do wonder whether or not the a/c captain was aware. I seriously doubt it.