The latest arrests came as Downing Street confirmed the launch of a new terror task force on extremism.
The group, of Cabinet ministers and top police and security service officials, will focus on radical preachers who seek out potential recruits in prisons, schools, colleges and mosques.
David Cameron has announced that the parliamentary Intelligence and Security Committee (ISC) will carry out an investigation following the disclosure that the two men suspected of murdering Drummer Rigby - identified as Michael Adebolajo, 28, and Michael Oluwatobi Adebowale, 22 - were known to MI5
.Authorities in France are also investigating whether the murder of Drummer Rigby was linked to an attack on a French soldier, who was stabbed in the neck in a busy shopping area near Paris yesterday.
Documents suggest Security Services were trying to recruit Woolwich suspect Michael Adebolajo and had also approached members of his family.
Police will today question one of the men suspected of murdering Drummer Lee Rigby in Woolwich, a week after the soldier's death.
After a three day search, I found the home of the grandmother of Michael Adebowale, one of the suspected killers of Drummer Lee Rigby.