A TEENAGER who brutally stabbed a policeman multiple times could be let off "lightly" after judges this week quashed his indefinite jail sentence.

Alister Gregson, from Purley – who was 18 when he "destroyed" PC Nigel Albuery's life – was jailed indefinitely at Kingston upon Thames Crown Court last August after pleading guilty to wounding with intent.

But judges at the Court of Appeal on Tuesday overturned the sentence, meaning the vicious thug could be released after just six years behind bars.

Gregson, of Whitfield Avenue, launched the relentless knife attack while PC Albuery performed a routine stop-and-search on the youngster in Bute Road, Waddon, in May 2011.

Peter Smyth, chairman of the Metropolitan Police Federation and and officer for 35 years, said: "If they are prepared to stab a police officer four times, that's as close to attempted murder as I can possibly think of, and that he was carrying a knife at the time would suggest he should have a substantial custodial sentence.

"He was obviously a dangerous person who showed no compunction about that sort of action.

"There needs to be a deterrent element and a punishment element in this type of sentence. Six years – I think that would mean he has been let off a bit lightly for what is obviously at the top end of assaults."

Gregson, now 19, was with three other youths when PC Albuery and a colleague approached the group on May 19, 2011, at 9.45pm.

But during the stop-and-search the teenager attempted to escape, before stabbing the officer four times in the back, shoulder and arms. The other three youths were arrested and released without further action.

Gregson also pleaded guilty last year to actual bodily harm after attacking his ex-girlfriend with a brick.

His indefinite sentence was substituted for a 14-year extended jail stretch – with a 12-year custodial term and two-year release on licence term.

But the sentence means he would qualify for automatic release, and is likely to be let out after six years.

Following the stabbing, brave PC Albuery said: "On May 19, 2011 my life was turned upside down by the unprovoked actions of Mr Gregson when he tried to end my life. I enjoyed my job and looked forward to coming to work.

"I made plans for my future career and also plans with my family. At approximately 9.45pm that night it all changed.

"I was stabbed four times and it has destroyed my confidence and upset all those plans.

"Due to the injuries received I had to spend several nights in hospital many miles away from my family in incredible pain. I have also suffered scars that will be a constant reminder to me and my family of what happened."

England and Wales Police Federation vice-chairman Simon Reed said: "A police officer is attacked about every 20 minutes.

"We need effective deterrents so that people will think twice before attacking an officer.

"We have always asked that 'the sentence should fit the crime', and it would be interesting to hear what local people believe to be an appropriate sentence for a man who repeatedly stabs an officer."