Matthew Feargrieve, a solicitor specialising in corporate and investment funds law, was sentenced this week after being found guilty of common assault last month, MyLondon reports.

He was found to have punched fashion designer Ulrich Engler “at least once” after he took a seat next to Mr Feargrieve’s wife.

Sentencing him in City of London Magistrates’ Court, District Judge John Zani told Mr Feargrieve: “It was excessive. It should not have happened. You are an experienced, professional man and you should know how to behave.”

Mr Feargrieve was fined £900 and ordered to pay £775 in costs, £500 in compensation and a £90 victim surcharge.

Mr Engler earlier told the court that he had moved from his second-row seat to a vacant front-row seat in a previous performance in Royal Opera House and decided to do so again.

He said asked Catherine Chandler if he could take the empty seat next to her and she said no, but admitted that she had not paid for it, so he moved into it anyway.

He removed Ms Chandler’s coat from the seat and put it on her lap and Mr Feargrieve then leaned over her and began hitting his shoulder, The Guardian reports.

Mr Engler was then arrested and temporarily banned from the opera house, though the case against him was dropped within weeks.