A teenager was snared by secret agents as he plotted a bomb attack, possibly targeting an Elton John concert in Hyde Park on the anniversary of the 9/11 attacks.

Haroon Syed, 19, from Hounslow, west London, pleaded guilty on Thursday at the Old Bailey to a charge of preparation of terrorist acts between April and September last year after a last-ditch attempt to get his case thrown out failed.

The court heard how Syed tried to get weapons online, including a bomb vest or explosives, and trawled the web to find a busy area in the capital such as Oxford Circus to launch a mass casualty attack.

Syed was caught chatting online with officers from the British Security Service who posed as a fellow extremist who could help him source the weapons.

Judge Michael Topolski QC adjourned sentencing until June 8 for a probation and psychiatric report to be done. He said Syed faced a "discretionary life sentence".

As Syed was being drawn in by agents, his older brother was jailed for plotting an Islamic State-inspired Poppy Day attack.

At an earlier hearing, the court heard how key evidence was gathered from Syed's communications with the fake contact Abu Yusuf via mobile phone and social media.