Family members of Lee Rigby speak at a press conference at the Regimental HQ of his unit, the Royal Regiment of Fusiliers in Bury

Lyn Rigby, right, the mother of murdered soldier Lee Rigby, is supported by her daughter Sara McClure while the family reads a statement

Rebecca Rigby, the wife of murdered soldier Lee Rigby, wipes her eyes during a family press conference in Bury, Greater Manchester

The scene at the junction of Artillery Place and John Wilson Street which has become a shrine to Drummer Lee Rigby

Police close a road in Saxilby, Lincolnshire leading to a house which was raided in connection with the attack in Woolwich (PA)

This video grab, from ITV News, shows two men being detained by police in John Wilson Street, Woolwich (ITV News/PA)

People leave flowers at the scene of the murder at the junction of Artillery Place and John Wilson Street in Woolwich

Lee Rigby, 25, from the 2nd Battalion, Royal Regiment of Fusiliers, was hacked to death in Woolwich (MoD/PA)

A man weeps outside the Royal Artillery Barracks in Woolwich as he looks at floral tributes following the attack on Lee Rigby (PA)

Ministry of Defence undated handout photo of Drummer Lee Rigby, 25, from the 2nd Battalion, Royal Regiment of Fusiliers who was named today as the soldier hacked to death in Woolwich yesterday. PRESS ASSOCIATION Photo. Issue date: Thursday May 23, 2013. See PA story POLICE Woolwich. Photo credit should read: MoD/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder.

LONDON, ENGLAND - MAY 23: A soldier stands in the rain as security is tightened around Woolwich Barracks on May 23, 2013 in London, England. A British soldier was murdered by suspected Islamists near London's Woolwich Army Barracks yesterday in a savage knife attack. British Prime Minister David Cameron has said that the 'appalling' attack appeared to be terror related. (Photo by Dan Kitwood/Getty Images)

A member of a mosque in Gillingham, Kent, boards up a smashed window after a man remains in police custody on suspicion of racially-aggravated criminal damage

Police have arrested an alleged friend of the Woolwich murder suspect Michael Adebolajo after he gave an interview to BBC Newsnight in which he claimed the security services had tried to recruit the suspect.

Abu Nusaybah told Newsnight that Adebolajo had informed him six months ago that the security service had been “knocking on his door”.

He said Adebolajo had told him he had turned down an offer to work for them. Mr Nusaybah said that his friend was “basically being harassed by MI5”.

In the interview he said: “His wording was, 'They are bugging me - they won't leave me alone.'

”He mentioned initially they wanted to ask him if he knew certain individuals.

“But after him saying that he didn't know these individuals, what he said was they asked him if he would be interested in working for them. He was explicit in that he refused to work for them but he did confirm he didn't know the individuals.”

Shortly after the interview it is understood Mr Nusaybah was met by police and remains under questioning.

Police last night confirmed that a 31-year-old man was arrested in London under the Terrorism Act 2000.

The man remains in custody at a south London police station. Search warrants are being executed at two residential addresses in east London.

Mr Adebolajo and fellow suspect Michael Adebowale, 22, of Greenwich, south-east London, remain in hospital after they were shot by armed officers following the death of Lee Rigby, who was killed in front of dozens of people in Woolwich, south-east London, on Wednesday afternoon.

Q&A: Could MI5 have done more to stop Woolwich attack?

Q. Are the attackers “lone wolves” or part of a wider network?

A. Both men mixed in radical Islamist circles, thus they had a wide circle of like-minded people around them. Two others have been arrested and questioned who appear to have social or family connections to the accused. The security agencies are indicating that it is unlikely a wider network was involved; this may change.

Q. Could MI5 have intervened to stop the attack? What information did the security services have?

A. The two men were known to MI5 as being involved on the fringes of militant activities and had been seen in the company of more serious terror suspects. But, it is claimed, they were not suspected of planning anything major. Officials admit they were caught unawares; thus they could not intervene. If this account of events unravels, MI5 will face severe criticism.

Q. Why did the first police on the scene stand back while members of the public spoke to the men?

A. The response time of the police and their immediate action has been the subject of criticism, claims and counter-claims. The situation which greeted them was extraordinary and somewhat surreal: men who had apparently just butchered another man, speaking relatively calmly to passers-by. Facing dangerous and armed suspects, they waited for firearms teams to arrive.

Q. How did the attackers meet?

A. This is unclear; but it seems they may have met through Islamist gatherings.

Q. Could a “snooper’s charter” have helped prevent the killing?

A. There is no evidence that it would have, and it is not something MI5 is claiming. The view of security officials is that communications intercepts would be of more use to the police in the early stages of an investigation to gather evidence on serious suspects.

Q. What was the precise nature of the contact between the alleged attackers and Omar Bakri Mohammed?

A. Michael Adebolajo attended sermons given by Bakri Mohammed, and among the questions he allegedly asked was when violence was permissible. Bakri Mohammed, who has since been banned from Britain, was once secretly recorded saying beheading was justified in defence of Islam.

Q. Can the failure to prevent the attack be attributed to a lack of resources?

A. More resources would give the security agencies the ability to carry out surveillance on more suspects. But it is still a matter of judgment on who to target. Total security is not possible in a democratic state and it would be unhealthy for a society if people were put under surveillance or harassed simply because they held unpalatable views.

Belfast Telegraph