Kane Johnston, 18, was given three years at Northampton Crown Court in June after he admitted assault, obstructing a constable, threatening behaviour and two ASBO breaches.

But following an appeal, three judges granted Johnston, of Rothersthorpe Road, Briar Hill, a one-year reduction in his "excessive" sentence.

Johnston was locked up after attacking a man during an argument in St John's Street, Northampton, in the early hours of February 14.

Steven Deakin had been part of a group who were arguing when Johnston turned up in a Vauxhall Corsa and got involved, knocking Mr Deakin momentarily unconscious with a punch to the face.

Two months later, he was at a birthday house party on April 5 in Arrowhead Road, Briar Hill, when police were called to arrest one of the party-goers for an unrelated offence.

Johnston, who was drunk, swore at and threatened the officers as they tried to enter.

He was heard shouting: "Get off my estate, you're going to get it and I'll glass you in the eye and you'll know about it."

Johnston later admitted being "cheeky" and swearing at the police, but denied attempting to stop them trying to arrest the suspect. Despite his young age, he already has a string of convictions for violence and offensive behaviour.

Judge Richard Bray, who sentenced him in June to two consecutive 18-month sentences, said: "A seriously aggravating feature of this case is your numerous previous convictions for assault, possessing offensive weapons, three offences of robbery, witness intimidation grievous bodily harm, wounding and assault."

But at the Court of Appeal yesterday, Lord Justice Scott Baker reduced the three-year sentence saying it was excessive. He added: "In our judgment, consecutive sentences were called for, but the sentence of three years in total is manifestly excessive."

Johnston is still subject to a new five-year ASBO banning him from causing alarm, harassment or distress and from drinking alcohol in public unless in licensed premises.