Police taunted the Muslim detainee, who has not been named, by forcing him to prostrate and asking him “where is your God now?”, according to his lawyer.
Mudassar Arani told Aljazeera.net on Wednesday that her client, of Pakistani origin, also suffered a black eye and bruising to his wrist, back, elbow and shoulder and that photographic evidence would be made available.
“Special Branch are responsible for inflicting physical and racial abuse on my client.”
Arani is representing another three people detained by police in London on Tuesday.
In total, security services arrested 14 people in central and southern England under the country's sweeping Terrorism Act 2000.
A policeman stands guard at the
gates of a mosque being searched
in the northern town of Blackburn
In addition to the four arrests in the capital, four men and two women were detained in Cambridge and four near Birmingham in the West Midlands.
Last week, Nur al-Din Muliff, a 36-year-old of North African origin, was arrested in the southern coastal town of Eastbourne.
He will appear before magistrates in London on Wednesday charged under section 57 of the Terrorism Act 2000, police said in a statement.
Section 57 deals with suspects found with "an article in circumstances which give rise to a reasonable suspicion that its possession is for a purpose connected with the commission, preparation or instigation of an act of terrorism".
The "article" found was not explosives, but security services would give no further details.
Police are allowed to hold suspects for seven days without charge.
Potential criminals and fear
The latest arrests come as police continue to question a suspected "potential suicide bomber" detained in the south western town of Gloucester last Thursday.
Britain has been on its second highest security alert for two weeks after intelligence officials said they had information an attack was planned, without specifying any target.
Prime Minister Tony Blair, speaking at his monthly news conference, played up the danger and stressed the very grave threat that Britons were under and urged vigilance.
"There's no doubt there is a threat because these people are operating in most parts of world and they have no compunction about taking the lives of innocent people," he said.
According to the London’s Metropolitan police, 250 Britons have so far been arrested under anti-terrorism laws and 70 charged.
But when contacted by Aljazeera.net, police could not provide information as to how many people had been successfully convicted.