Family of allaged London mosque attacker 'devastated'

The family of the man accused of mowing down Muslims outside a London mosque say they're "devastated" and called the attack "sheer madness".

The family of the man accused of the London mosque attack say they're "devastated". (AAP)

The family of a man suspected of driving a rented van into Muslim worshippers after they left prayers at a north London mosque say they are devastated at the "madness" of the attack.

The vehicle swerved into the group of worshippers, mainly of North and West African origin, after they left prayers in Monday's early hours at the Muslim Welfare House and the nearby Finsbury Park Mosque in north London, one of the biggest in Britain. Eleven people were injured.

Police said Muslims were clearly the target and Prime Minister Theresa May described it as a "sickening" terrorist attack.

A 47-year-old man was restrained by locals at the scene and police later arrested him on suspicion of attempted murder and terrorism offences. He is still being questioned by detectives, and will be held for another three days, police said.

Apart from 11 people injured, police were still looking into a possible link between the incident and one death at the scene.

The suspect was named by British media as Darren Osborne, 47, a father of four, who lived in the Welsh capital Cardiff

In a statement on behalf of his family, nephew Ellis Osborne said: "We are devastated for the families, our hearts go out to the people who have been injured. It's madness. It is obviously sheer madness."

The incident at Finsbury Park was the fourth attack in Britain since March and the third to involve a vehicle deliberately driven at pedestrians.

The previous attacks had been blamed on Islamist extremists.

An imam from the Muslim Welfare House who stepped in to protect the driver from the angry crowd after the incident was hailed as a hero in British newspapers on Tuesday.

"We found that a group of people quickly started to collect around him ... and some tried to hit him either with kicks or punches," Mohammed Mahmoud told reporters.

"By God's grace we managed to surround him and to protect him from any harm."

Security Minister Ben Wallace said the man was not known to the security services and police said they believed he was acting alone.

The British Press Association reported police had responded to reports of a "drunk man" sleeping in a van in Cardiff, who a witness now believes was Osborne, just 24 hours before the rampage.

Edward Gardiner called police just after midnight on Sunday morning to report concerns for the welfare of a man, who smelt of alcohol, sitting in a Pontyclun Van Hire vehicle.