Thanks for the reply.
The complaint was made as the train guard suggested he should do so as he felt the inspector was rude to my son and he said he would also send a report to his supervisor.
My son had the money and bought a ticket on the train.
In terms of the attitude test my son gave the correct details otherwise we wouldn't have received the letter.
The frustration is everyday I see people buying tickets on the train or paying at their destination station, I have done it several times this year. This is standard practice with Arrival trains, their signage says you should attempt