Four teenagers have been convicted of a series of violent crimes including an incident where a man had his nose sliced off with a machete.

Police say the teens were part of a gang that arranged drug meets in residential streets in St Albans and London Colney armed with machetes and swords.

The young men, who cannot be named for legal reasons, were found guilty of conspiracy to commit robbery and grievous bodily harm (GBH) following a six-week trial at St Albans Crown Court.

Police say most of the offences, which occurred between December 2019 and September 2020, happened in Clarence Park and other parts of St Albans, as well as in Cotlandswick in London Colney.

The offences covered in the conspiracy charge are GBH and robbery on December 9 2019 in York Road in St Albans; robbery on December 21 2019 in Artisan Crescent, GBH in Cotlandswick in London Colney on 13 January 2020 - which involved a man suffering a serious injury to his nose with a machete - and a robbery in Sainsbury’s in London Colney on September 23 2020.

Detective Sergeant Tom Evans, from the St Albans Local Crime Unit, said: "The escalation in violence at the end of 2019 into 2020 was so dramatic that we were gravely concerned there was a real risk that someone may be killed because they were carrying weapons including machetes and swords."

He added: "We are delighted that these teenagers were convicted today as they were dangerous, not just to others, but also to themselves.

"They arranged drug meets in residential streets armed with machetes and swords, which were witnessed by residents, including children, and taxi drivers."

A 19-year-old of no fixed address, two 18-year-olds from St Albans, and a 19-year-old from Welwyn Garden City will be sentenced at a later date.

A 17-year-old from London Colney was found not guilty of conspiracy to commit GBH and no decision was reached for the count of conspiracy to commit robbery, so a re-trial will be held for this matter.

The policing operation, called Operation Luge, involved police officers as well as St Albans City and District Council.

DS Evans added: "It was one of the biggest police responses to a series of incidents in St Albans. The investigation was unusual because the indictment is conspiracy (to commit GBH and robbery) rather than a list of charges.

"This was because we were unable to prove which teenager was responsible for the offences, but we knew they were all involved."

Police say the boys, who were aged between 16 and 18 at the time of offending, met at school in St Albans.

St Albans neighbourhood inspector Andy Wiseman said: "I hope this conviction reassures the community who were unfortunate to witness violence or see weapons in the city during 2020. There is no place for violence in this district.

"My officers are determined to bring offenders before the courts, even with Covid-19 delays, and see them held accountable for their actions with support from youth offending teams. We wanted a long-term solution to problems to make sure every resident can enjoy our parks and improve the community’s quality of life."

He added: "Please always contact us if you see anyone acting suspiciously, suspect drug dealing may be taking place or see any weapons. Rest assured we act on every piece of information we receive."