Two secret police officers broke their cover after they saw what looked like a multiple stabbing as a drug deal turned violent at a city park, a court heard.

The pair of plain-clothed officers had been watching the deal at a park off Rosary Road in Norwich on November 11 last year.

But they ran over to control the situation with PAVA spray when they thought that one man was being repeatedly stabbed.

Norwich Crown Court heard on Thursday how Nathan Tomkinson, who was brandishing the knife, had instead been hitting his victim.

The 40-year-old, of Magdalen Street in Norwich, was sentenced to 14 months in prison for affray and possessing an offensive weapon.

Prosecutor Jude Durr said undercover officers had been watching as the deal took place shortly before 2pm that day.

He told the court how Tomkinson, who arrived in a red van, approached one of the men from behind and put him in a headlock.

'There was a struggle, during which Tomkinson proceeds to produce a six-inch knife from his jacket,' he said.

Mr Durr said the defendant then hit the victim with his fist which was holding the knife at the time. 'Both observing officers thought this was a stabbing taking place in front of them,' he said. 'They broke cover and approached the action taking place.'

Tomkinson, who has 86 convictions for 213 different offences, was then arrested by officers. He initially pleaded not guilty to affray and possessing an offensive weapon, and was due to go on trial on Thursday.

But prior to him appearing in court, wearing a jumper and shirt, he admitted the offences.

Mr Durr said Tomkinson's criminal record ranged from drug offences and theft to burglary.

Paul Roach, mitigating, said his client was 'adamant' he would not have stabbed anyone and had previously been injured by a knife.

'He picked it [the knife] up when he realised who was there,' Mr Roach said.

'Had he meant to stab someone, he would have injured them, and there were no injuries.'

Judge Katharine Moore said Tomkinson had already spent five months in custody. 'You may well insist you were not intending to cause injury with the knife, but you cannot account for the actions of others,' she said.