FF
The right to leave the UK is something to which you are entitled, it is not a privilege. There are many 20th century examples of societies which did limit the movements of their citizens, the one which springs to mind is the USSR, though there are others.
Getting back to the subject of this thread, the person in question was dealt with by the courts and was sent to prison for 12 months. Personally, I think this is an appropriate punishment. Violent conduct is unacceptable, especially when the victim is simply doing their job, on this occasion the Court agreed and I think everyone should be satisfied with the end result.