A teenager has been sentenced to three years in prison after admitting to marking bombs threats to thousands of schools across the country – including in Herts and Beds.

In September, George Duke-Cohan – aged 19 and from Watford – pleaded guilty to three counts of making hoax bomb threats at Luton Crown Court, where he returned for sentencing on Friday.

The teenager sent bomb threats that resulted in more than 400 schools being evacuated in March, and was arrested days later.

Among those who received the mass email threat were The Valley School in Stevenage, St Albans High School for Girls and Samuel Ryder Academy in St Albans.

In Bedfordshire, Sandy Upper School, Fairfield Park Lower in Fairfield, Roecroft School and Pippin Pre-School in Stotfold all evacuated after receiving the threat.

While under investigation in April, Duke-Cohan sent a mass email to schools in the UK and the US claiming that pipe bombs had been planted on the premises.

As well as the bomb threats made to schools, he was also responsible for a threat made to a United Airlines flight travelling from the UK to San Francisco in August.

In a recording of one of the phone calls which was made while the plane was in the air, he takes on the persona of a worried father and claims his daughter contacted him from the flight to say it had been hijacked by gunmen, one of whom had a bomb.

On arrival in San Francisco the plane was the subject of a significant security operation in a quarantined area of the airport. All 295 passengers had to remain on board causing disruption to onward journeys and financial loss to the airline.

The National Crime Agency’s senior investigating officer Marc Horsfall said: “George Duke-Cohan carried out these threats hidden behind a computer screen for his own enjoyment, with no consideration for the effect he was having on others.

“Despite being arrested and having conditions imposed restricting his use of technology, he persistently broke those conditions to continue his wave of violent threats.

“Law enforcement take such offences extremely seriously. The sentence handed down to Duke-Cohan highlights the consequences of such offending.

“This investigation proves that operating online does not offer offenders anonymity. Duke-Cohan now has a criminal record which will harm his future career prospects and this should act as a deterrent to others.”