Five men were arrested by police investigating inflammatory Muslim protests last month at the Danish embassy over cartoons which satirised the Prophet Mohammed.
All five were held on suspicion of inciting racial hatred and four of them on suspicion of incitement to murder.
One of those arrested on both grounds is Anjem Choudary, 38, the former UK head of Al-Muhajiroun, the radical Muslim group, and a close associate of Omar Bakri Mohammed, the Islamic cleric who is currently in Lebanon and barred from Britain.
Mr Choudary is a prominent figure in Al-Gurabaa (The Strangers), a group set up by supporters of Bakri, which led the cartoon demonstrations.
The arrests—four in London and one in the West Midlands—follow the protests outside the Danish Embassy in London on Feb 3, when placards threatening a repeat of the September 11 or July 7 terror attacks were waved. Scotland Yard detectives have been studying video, photographs and sound recordings of the demonstration, including CCTV footage.
There were a handful of complaints from eye witnesses and around 500 from those who saw pictures of the demonstration.
The Crown Prosecution Service (CPS) advised police there were sufficient grounds for prosecutions. Police are still trying to identify some suspects.
Placards seen on the demonstration bore messages such as “Massacre those who insult Islam”, “Europe you will pay” and “Europe you’ll come crawling when Mujahideen come roaring”. Police were criticised in some quarters for not making arrests at the time.
The shadow Home Secretary, David Davis, said yesterday: “Whilst it has taken five weeks to get to this point, it is entirely right that action should be taken against whoever it was that effectively incited murder outside the Danish embassy.”