A British teenage Islamist was on Monday jailed for a minimum of 16 years for plotting a bomb attack at an Elton John concert in London on the 9/11 anniversary.

Judge Michael Topolski at London's Old Bailey said Haroon Syed, 19, was "committed to carrying out an act of mass murder" as he handed down the life sentence with a minimum 16-year term. 

Syed, from west London, admitted in April that he was preparing terrorist acts between April and September last year, considering targets such as London shopping destination Oxford Street and John's concert in Hyde Park on the 15th anniversary of the attacks on the United States.

Around 50,000 attended the central London concert, which also featured a performance by British ska band Madness. 

The court earlier heard that Syed had become influenced by members of Al-Muhajiroun (ALM), a banned group linked to radical preacher Anjem Choudary.

"You were not lured, you were not enticed, you were not entrapped," said the judge.

"You became deeply committed to the ideology of a brutal and barbaric organisation," he added.

Syed admitted trying to get a machine gun, handguns, suicide vest and bomb, London's Metropolitan Police said following his guilty plea.

"When he couldn't raise any finance through loan applications, settled on trying to source a bomb, with a special request for it to be packed with nails so he could detonate it in a crowded place."

He told a Security Service fake contact that he needed a machine gun and an explosive vest "so after some damage with machine gun do martyrdom... that's what I'm planning to do.

"You have to find out the price for the machine gun, any gun."

On August 30 last year, he said: "I might put the bomb in the train and then I'm going to jump out so the bomb explodes on the train."

He arranged to buy a custom-made bomb and asked his contact to make sure it contained lots of nails.

"I was thinking of Oxford Street... If I go to prison, I go to prison. If I die, I die, you understand," he said.

His search for potential locations included John's concert.

When he was arrested on September 8, he told police his phone password was ISIS, an acronym for the Islamic State jihadist group.

Syed's brother, Nadir Syed, 23, was jailed for life with a minimum term of 15 years last year after being found guilty of plotting to carry out a beheading of a serviceman around Remembrance Sunday in 2014.