Four “dangerous” teenagers who sparked fear and violence during a series of knife offences have been jailed.

The gang committed knife point offences over 10 months between December 9, 2019, and September 2020 across St Albans and London Colney.

This includes an incident where a man in his 20s had his nose sliced off with a machete on January 13 last year.

Other offences included grievous bodily harm and robbery on December 9, 2019, at York Road in St Albans, a robbery on December 21 that year in Artisan Crescent and a robbery in Sainsbury’s in London Colney on September 23, 2020.

The group were sentenced to a total of 42 imprisonment, with three of them receiving 12 years imprisonment with a further five years on licence.

They are:

• Kai Henry-Smith, 18, of Maynard Drive in St Albans, who previously pleaded guilty to a GBH wounding with intent and possession of a machete that happened in Grindcobbe in St Albans on 4 November, 2020. His sentence will run concurrently.

• Harvey Kavanagh, 17, of Willoughby Court in London Colney.

• Isaac Wallace-Greaves, 18, of Cottonmill Crescent in St Albans.

The fourth teenager, Kobi Nelson, 19, of De Parys Avenue in Bedford, received a six-year custodial sentence for the robbery in Artisan Crescent.

The boys, who were aged between 16 and 18 at the time, met at school in St Albans.

St Albans Detective Inspector Ady Lysak said: “These offences were predetermined, organised and executed with the goal of trying to exert their authority over drug operations being run in St Albans. This gang were inflicting serious injuries at knife point and stealing from their victims.

“These teenagers were dangerous, not just to others, but also to themselves. They arranged drug meets in residential streets armed with machetes and swords, which was seen by families, including children.”

The investigation was overseen by Detective Sergeant Tom Evans, who said: “There was a genuine and significant escalation in violence which was so dramatic that there was a real and significant risk that someone may have been killed. We are thrilled that these individuals are now behind bars and that residents in St Albans and London Colney can go about their daily business without the fear of violence hanging over them. It was one of the biggest police responses to a series of incidents in St Albans.”

When sentencing Kavanagh and Wallace-Greaves, HH Judge Richard Foster said: “You behaved like a savage when you carried out that merciless attack on the victim at Cotlandswick. It is hard to understand how one human being can behave in such a way to another. The victim suffered devastating injuries. These included multiple lacerations from the forehead extending to the back of the head, a fractured skull, the amputation of the tip of his nose….partial amputation of the middle finger and the full amputation of the left ring finger.”

He said: “The armoury of weapons and other items found during the police investigation is truly horrifying, including multiple large knives.

“It took some astute police work to link together a number of what would have seemed initially as separate criminal incidents in this city of St Albans. I commend the police investigation team – particularly officer in the case DC Perrin.”