A terror suspect arrested just yards from Downing Street with a rucksack full of knives took part in a controversial aid convoy to Gaza, it has emerged.
Khalid Mohammed Omar Ali, 27, was one of seven Britons on board a ship that was trying to deliver humanitarian aid to Palestinians during the Israeli blockade in 2010.
Fellow aid workers described him as a "quiet and peaceful man" who was always smiling and was driven to help others.
In a video that emerged from the convoy, Mr Ali can be seen sitting in the front of a van with a Palestinian banner tied around his head.
Speaking excitedly about his impending trip he says: "We are all getting together now, alhamdulillah, the vans are all done, energy is here, the sunshine is here, alhamdulillah [praise god]... "You are going to see in action - the youth - doing our thing, all day long. We did it in Tottenham, we are going to do it in Gaza; taking it to another level. One love."
But his experiences delivering aid to war torn areas may have left him disturbed and possibly suffering from some form of post-traumatic stress disorder, one former associate said.
Mr Ali, who was born overseas, but brought up in Tottenham, north London, was detained by armed officers in Westminster on Thursday afternoon, as part of a planned counter-terror operation.
It is understood police had been watching him for sometime after receiving a tip off from his family, who had become increasingly concerned about his erratic behaviour.
Seven years ago he was among of a group of volunteers from the Road to Hope charity, who attempted to take food, clothing and other supplies to Palestinians aboard a Maltese registered ship, the Strofades IV.
The mission was launched just months after Israeli commandos had stormed a flotilla of ships trying to break the naval blockade of Gaza, killing nine activists.
Mr Ali was one of ten aid workers, who set off from Libya bound for Gaza in November 2010.
But they ended up becoming stranded in the Mediterranean following a row with the ship's owners over money.
Rather than sailing for Israel, the captain headed for his native Greece, where the aid workers were reportedly held against their will.
According to one of the volunteers, Tauqir Sharif, from Walthamstow, the captain branded the group "terrorists".
The matter was later resolved and the volunteers returned to the UK.
One of the group, who asked not to be named, remembered Mr Ali as a happy and friendly person, who showed no signs of radical beliefs.
He said: "Khalid was a happy, smiley person who was very easy going. He had a genuine desire to help people. But perhaps his experiences took their toll on him and he has suffered some sort of post-traumatic stress disorder."
Police and the members of the security services are understood to have been watching his movements after a member of his family raised the alarm amid heightened concern over his recent behaviour.
Mr Ali's arrest in Westminster came just five weeks - and a 100 yards away - from the spot where Khalid Masood was shot and killed after launching a deadly terror attack.
Witnesses described armed police pinning him to the ground as he made his way along Whitehall in the direction of Downing Street.
Although he had been under surveillance he had been able to travel into central London by Tube before eventually being apprehended.
A senior policing source said: “He was being watched very closely. He had been travelling on the London Underground and we understand he had exited the Tube at St James’s Park station before walking in the direction of Whitehall and Number 10.
“At some stage an alert went out to all the teams in the area and the order was made to pick him up.”
It is not clear if police knew he was carrying weapons when the decision was made to stop him.