Britain’s youngest Islamist terrorist is back behind bars for breaking his release conditions after being jailed for plotting a beheading and massacre aged just 14.

The man, from Blackburn, Lancashire, identified only by the letters RXG, was described as a “deeply committed extremist” who, aged 14, was days away from helping stage a “massacre” at an Anzac Day parade in Australia in April 2015.

Six months later he was sentenced to life at Manchester Crown Court and told he would only be eligible for parole in October 2020 after serving a minimum of five years in custody after admitting inciting terrorism overseas.

He was arrested last month and, now in his early 20s, is back in custody at a jail in the north of England, security sources told the PA news agency.

RXG was found to be in possession of a smartphone, which broke the terms of his release on licence.

The nature of the material on his phone is not known to PA but sources said the fact that he had the internet-enabled device meant he was held.

RXG had exchanged more than 3,000 encrypted messages from his Samsung phone instructing a jihadist in Australia, Sevdet Besim, to launch “martyrdom” attacks during an Anzac Day remembrance parade in Melbourne.

The teenager was recruited online by Islamic State propagandist Abu Khaled al-Cambodi and took on the role of “organiser and adviser”, suggesting to Besim beheading or using a car and machete to murder police officers.

Australian police were alerted to the plot after British officers discovered material on the teenager’s phone.

Media are banned from identifying RXG so as not to interfere with his rehabilitation.

Anzac Day parade terror court case
A ‘Rambo’ knife, replica of the knife featured in the film First Blood, which RXG and Sevdet Besim discussed online prior to their arrests (GMP/PA)

A Probation Service spokesman said: “Protecting the public is our number one priority so when offenders breach the conditions of their release and potentially pose an increased risk we don’t hesitate to return them to custody.”

There is no suggestion he has committed any further offences.

Sources said RXG had already had one “close shave” on being recalled to prison, after he was located near an airport.

When he was jailed at Manchester Crown Court in October 2015, one expert concluded the defendant posed a high risk of serious harm to the public including forces and emergency service personnel worldwide.

Jailing him, Mr Justice Saunders said the revelation that someone of only 14 was radicalised to the point of wanting to murder was “chilling”.

The court heard the defendant felt isolated in terms of his education and home life, and filled the “vacuum” in his life with religious extremism.

He had paid “lip service” to the Government’s attempts to deradicalise him through the Channel programme and became “disengaged” with the process.

Police found “disturbing material” on electronic devices seized from his bedroom.

An officer from the hi-tech unit of the North West Counter Terrorism Unit (NWCTU) decoded the encrypted messages exchanged and uncovered the plot.

Anzac Day was the chosen for the attack as it is commemorated each year on April 25, to honour Australians and New Zealanders killed in war.

Besim, at the time 18 and from Melbourne, pleaded guilty to a single terror-related charge and was jailed for 10 years at the Victorian supreme court in 2016.

A ban on identifying RXG because he was aged under 18 applied at the time he was convicted.

The ban would normally expire on his 18th birthday but he successfully won a High Court ruling in 2019 giving him anonymity for life after media tried to name the defendant.

The judge said experts had concluded that identifying RXG would “fundamentally undermine” his rehabilitation.