An investigation has been ordered into how a protester managed to burst into the Leveson Inquiry as Tony Blair was giving evidence and yell: “This man should be arrested for war crimes.”
The intruder, who told reporters his name was David Lawley Wakelin, managed to evade security and access the court room through a back corridor.
The 49-year-old, who made a film called The Alternative Iraq Enquiry, brought proceedings to a halt by hurling accusations at the former Prime Minister.
He said: "JP Morgan paid him off for the Iraq war. Three months after he invaded Iraq they held up the Iraq bank for 20 billion.
"He was then paid six million dollars every year and still is from JP Morgan six months after he left office.
"This man is a war criminal."
He was eventually wrestled to the ground by three men, ejected from the courtroom and arrested.
Lord Justice Leveson, who rose to his feet when the intruder entered dressed in white shirt and trousers, called for an immediate inquiry into how he had got in.
"I would like to find out how this gentleman managed to access the court through what's supposed to be a secure corridor, and I'll have an investigation undertaken about that immediately," he said.
After the removal of the protester Mr Blair denied his allegations.
He told the hearing: "What he said about Iraq and JP Morgan is completely untrue. I've never had a discussion with them about that."
After leaving office Mr Blair advised the investment bank in return for a reputedly giant pay packet.
The protester was escorted through the Royal Courts of Justice by security guards and was seen being driven away in a police van.
It is understood he got past security-coded doors to access the judges' corridor leading to courtroom 73.
Scotland Yard said he was arrested on suspicion of breach of the peace and was held in custody at a central London police station. He was released without charge.
Mr Lawley Wakelin said later that it was "surprisingly easy" to get into the court.
He told James O'Brien on LBC 97.3: "I just went ... up the back stairs and found that there was no security at all and in fact the door to the court was wide open in the same way that Lord Leveson himself would have got in there."
It was "a little unnerving" to find himself suddenly in the spotlight, he said, but that he decided his "beef with Tony Blair is too great to miss this opportunity".
The police asked him to stay away from the rest of the Leveson Inquiry and he intended to obey that order, he said.
"My only beef is with Tony Blair and nothing to do with the Leveson Inquiry," he added.
A spokesman for HM Courts and Tribunals Service (HMCTS) said the service took security very seriously at all of their venues.
"An investigation has been ordered into an incident at the Leveson Inquiry, Royal Courts of Justice, today," a spokesman said.
"It would be inappropriate to pre-empt the findings of this investigation."
When the hearing reconvened for the afternoon Lord Justice Leveson told the court that the inquiry and HMCTS took the incident "extremely seriously" and apologised for the breach.
He said: "Considerable effort has been put into ensuring all witnesses can give their evidence in a safe and secure environment and I very much regret what has happened.
"An investigation is being undertaken and I will be giving consideration to the steps that can be taken and should be taken against this particular intruder. Efforts will be redoubled to ensure that incidents of this nature don't recur.
"I repeat my apologies to Mr Blair and indeed to everyone else who was involved in or following our inquiry."
Mr Blair appeared unfazed by the shock interruption of his evidence.