A supergrass who-se evidence helped convict the Leigh allotments murderer has been sentenced to five years in prison.

Damon Alvin, 33, formerly of Rushbottom Lane, Benfleet, pleaded guilty to conspiracy to pervert the course of justice, burglary, conspiracy to steal, possession of a firearm with the intent to commit an indictable offence and two counts of causing grievous bodily harm. He was told he must serve at least half of the five-year sentence.

He testified against Ricky Percival, who was convicted last month of murdering Dean Boshell in 2001.

Alvin was originally charged with the murder at the Manchester Drive allotments and has been in custody since October 2004. This means he has served almost half his sentence and could be free within months.

He came clean in September 2005 and during extensive police interviews admitted his involvement in other crimes with Percival, including a triple shooting in Southend and the robbery of the Wickford Snooker Club.

Judge Christopher Ball QC sentenced Alvin yesterday at Chelmsford Crown Court.

He said: "You took an extraordinary step in confessing what you had done over many years.

"It is in the public interest that what you have done should be recognised as a very dangerous offender has been convicted. The public is now safer for what you have done."

On December 15, Per-cival, 27, of Cricketfield Grove, Leigh, was sentenced to 26 years in prison for the murder of Dean Boshell.

Percival was also convicted of three attempted murders in 1999 after he burst into a house in Locksley Close, Southend and fired at members of the Tretton family.

During his trial, evidence was given that Mr Boshell, 24, of Elmsleigh Drive, Leigh, was a police informant. He was shot three times in the head at point blank range.

Mitigating for Alvin, John Black, QC, said: "In doing what he did, Mr Alvin crossed the Rub-icon, in that there was no turning back. He had to turn his back on everything that had been his way of life.

"What he has done will create enormous problems for him and his family. He will be looking over his shoulder for the rest of his life because there will be people that are less than impressed that he has given evidence for the Crown."

During Percival's 11-week trial, allegations of organised crime, bribery and police corruption emerged.