A teenager who ‘stabbed people for fun’ when a water fight in Hyde Park exploded into violence is facing years behind bars.

Joshua Clements, 18, stabbed two men with a hunting knife after thousands of people gathered in the park in central London to enjoy the warm weather on 19 July.

Shocking footage, taken on an onlooker’s mobile phone, captured the attack on Audean Thompson - which was considered so serious Clements was initally charged with attempted murder.

Today, as Clements pleaded guilty to a lesser charge, Judge Michael Topolski QC demanded an explanation from prosecutors why they chose not to pursue a trial for attempted murder.

Joshua Clements attacked several people with a hunting knife while wearing a sinister mask (left). Today Clements (right) pleaded guilty to wounding with intent

He said prosecution papers ‘revealed the horror of what was going on that evening in Hyde Park’ but adjourned the case for sentence for reports to be prepared.

Judge Topolski said: ‘This is not, on the face of it, just stabbing in the course of robbing, it was stabbing for fun going on.

‘I just wonder if this defendant may be a life candidate. He is terribly young and terribly dangerous.’

He added: ‘To say this is a disturbing case is an understatement.'

This is the hunting knife Joshua Clements brought to Hyde Park on July 19 and used to stab several people. A judge said it was 'stabbing for fun'

People had gathered in the afternoon on July 19 for a spontaneous water fight but violence erupted as police tried to disperse the 4,000-strong crowd.

As the mood turned, some began throwing bottles at officers - one of whom was stabbed in the hand - while violent clashes erupted amid chaotic scenes.

Appearing by videolink at the Old Bailey, Clements admitted wounding with intent over the attack on Mr Thompson, and pleaded guilty to a similar offence in relation to his second victim, Duane Williams.

Clements also admitted possessing a hunting-style knife, handling a stolen ring and Armani pouch, as well as possessing crack cocaine and heroin with intent to supply.

A Metropolitan Police officer and two members of the public were knifed and four other PCs were injured after a water fight and party in Hyde Park, central London, spiralled out of control

Philip Stott, prosecuting, said: ‘Those pleas were indicated in advance and they are accepted.’

But he was told by the judge: ‘The public need decisions such as the one made in this case explained to them.

‘I hope it is explained to the victim fully. The public demands, through me and these courts, an explanation.

‘That is why there will need to be one. I have no doubt it is for good reasons. You will have to set them out in detail.’

Police sealed off the whole area and cancelled police leave after the disorder on July 19

Referring to Clements' criminal record, the judge said: ‘This young man has been convicted of robbery, of battery, of robbery again, possession with intent to supply heroin, possession with intent to supply crack cocaine, possession of a knife in a public place, failing to comply with the requirements of a youth rehabilitation order. And all of that before he leaves the youth court.’

He warned Clements: ‘In one sense, one decision has already been made. You are facing a very significant term of detention. You understand that don’t you?’

The defendant answered: ‘Yes sir.’

Forensic officers at the scene of the disturbances in Hyde Park on July 19, when a water fight descended into violence and three stabbings

Judge Topolski added: ‘The question is how long and that’s a question I am far from able to decide today.’

Clements, from White City, west London, pleaded guilty to two counts of wounding with intent, possession of a knife, two counts of handling stolen goods, and two counts of possession of crack cocaine and heroin with intent to supply.

He was remanded in custody before sentencing on October 6.