An internet firm could have helped prevent the brutal murder of Lee Rigby, according to a parliamentary watchdog.

The US web firm- reported to be Facebook- has been criticised for failing to notify law enforcement agencies after Michael Adebowale used the site to contact an extremist known to have links to Al-Qaeda, expressing his desire to murder a soldier.

Adebowale, Mr Rigby's murderer, vowed to slay a soldier in an exchange sent five months before he committed the act with accomplice Michael Adebolajo, according to a report from the Intelligence and Security Committee.

Addressing a press conference in parliament, Sir Malcolm Rifkind, who chaired the report, said the web firm could have made a difference by notifying law enforcement agencies of the online exchange.

He also said: "This was highly significant.

“Had MI5 had access to this exchange at the time, Adebowale would have become a top priority.

"There is, then, a significant possibility that MI5 would have been able to prevent the attack.

"However, this company does not regard themselves as under any obligation to ensure that they identify such threats, or to report them to authorities.

"We find this unacceptable - however unintentionally, they are providing a safe haven for terrorists."

News Shopper: Michael Adebowale

Lee Rigby killer Michael Adebowale

Adebolajo and Adebowale ran over Mr Rigby who was raising funds for Help For Heroes whilst driving at 40mph, before attempting to behead him.

The 192 page report from the Intelligence and Security Committee also criticised MI5's investigation of Adebowale, where it took them three months to identify him as a person with extremist material and five months before action was taken.

MI6 also came under fire for failing to take significant action in response to Adebolajo's arrest in Kenya in 2010, when he was stopped under suspicion of attempting to travel to Somalia to join the terrorist group Al Shabaab.

MI6 were notified of the arrest but did not seek to interview Adebolajo or ask to be involved in any interviews by Kenyan Authorities.

10 things we've learned from the Lee Rigby murder security service report