The son of Stagecoach tycoon Brian Souter has been fined £600 after an attack on two men at a graduation party.

But Scott Souter, 21, escaped a jail sentence after writing a private letter to a sheriff.

Sheriff Robert McCreadie imposed the fine yesterday after hearing Souter – who has previous convictions for assault and joyriding – had paid £700 to his victims.

He took the extraordinary step at an earlier hearing of asking Souter to pen him a private letter, which would not be read out in open court, explaining why he drank to excess.

Sheriff McCreadie spent several minutes reading the lengthy letter and said: "It is a very helpful and articulate letter, which is what I expected from you. I thank Mr Souter for doing that. I am pleased for you," he told him.

"It is confidential to me and that is how it will be treated.

"I wanted to make him reflect on his own behaviour and that can be done particularly well if somebody is made to write out their situation. If this court has helped you I am pleased."

Perth Sheriff Court heard how Souter – who works in social media for Stagecoach – attacked the men after they frowned at him and he admitted he had been battling a serious drink problem.

Souter had drunk so much in Roca Blu – a 1980s theme pub in Perth – that he had little memory of what he did and claimed he might have been having a hypoglycaemic episode.

He attacked the men shortly after meeting them in Roca Blu, where Kara McKillop was holding her graduation party on June 30 last year.

Souter, of Perth, admitted attacking Keith Dewar, 23, by punching him on the head and body to his injury. He also admitted attacking and injuring Drew Fleming, 22, by punching him on the face.

Mr Fleming sustained a broken nose. Souter paid Mr Fleming £500 and Mr Dewar £200 as compensation.

The millionaire's son faced a third charge, of attacking Miss McKillop by punching her on the head, but it was dropped by the Crown.

Fiscal depute John Malpass told the court: "All persons present were under the influence of alcohol and for no apparent reason the accused began punching Mr Dewar.

"They had only met that night. He punched him on the head. This was observed by Mr Fleming, who intervened, and the accused punched him on the face."

Sheila McCall, defending, said her client had an alcohol problem and that his family were in a position to pay privately for treatment to help him.

She told the court: "He has deep regret over his behaviour and wishes to apologise unreservedly to these two young men."

She said a psychiatrist had ruled that "there may well have been a hypoglycaemic episode because of the sheer quantity of alcohol taken".

Mrs McCall said: "He has a stable family. There is support there. There has been parental involvement in discussions about these proceedings.

"He has some vague memory of these two gentlemen looking at him and perhaps frowning at him. That is the only recollection of these two chaps that evening."

Sheriff McCreadie said: "No doubt, at the age of 21, he thinks he is immortal. Some people just can't drink. When they start to drink they can't stop.

"They end up blotto and comatose and have no memory of events. Do you not want to live a long and prosperous life? Of course you do, so why prejudice everything to go out with your pals and get blotto? What on earth do you think you are doing?

"You look like an intelligent man so behave in an intelligent way. You have got to be able to say no. You have an equally important duty to yourself and your family. You are in a position to do something about it. I want to see a life free of booze."

In 2009, Souter was fined £200 and ordered to pay £400 compensation after raining blows on a stranger who taunted him about his father at a party.