Darren Manning-Coe (19), of 4 Ancar Road, admitted causing actual bodily harm to Sgt Andrew Coller in Norfolk Street, Lynn, on June 7.

After the hearing at Lynn Magistrates' Court, Norfolk Police issued a statement deploring the attack and pledging to bring perpetrators of such acts to justice.

Manning-Coe also admitted using theatening words or behaviour in Chicago's nightclub for which the magistrates imposed no separate penalty.

Hugh Cauthery, prosecuting, said Sgt Coller, an officer with 15 years' experience, was on public- order patrol with other officers at about 2.45am.

He saw Manning-Coe squaring up to two taller men and went over with other officers to separate the parties. After making inquiries into an alleged assault, Sgt Coller arrested Manning-Coe, who suddenly shouted and punched him extremely hard in the face, knocking him to the ground with blood gushing from his nose, said Mr Cauthery.

He was taken to hospital, detained overnight and suffered pain, bruising and swelling for three weeks, during which he also missed two family celebrations, said Mr Cauthery.

When interviewed, Manning-Coe said he recalled going out with friends and drinking five pints of beer in a bar before having more to drink, including shots, at Chicago's.

After being ejected, he vaguely remembered being spoken to by the police but did not remember the assault, said Mr Cauthery.

The magistrates watched a CCTV recording of the attack and were shown photographs of Sgt Coller's injuries.

After reading pre-sentence reports, they heard from Ben Pearson, for Manning-Coe, that his client pleaded guilty at the earliest opportunity.

He said Manning-Coe knew it was very likely he would receive a custodial sentence, bearing in mind the aggravating features in the case, his statements and previous convictions.

A Norfolk Police spokesman said: "The role of our police officers is to support, work with and protect the public and we deplore any type of assault against them.

"This case clearly shows that action will be taken against anyone who attacks our officers to secure a prosecution and bring the perpetrators to justice."