The man responsible for killing four people and injuring dozens used techniques that police say were "low sophistication, low tech, low cost."
British police said on Monday they had found no evidence that Khalid Masood, who killed four people in an attack on Britain's parliament last week, had any association with Daesh or Al Qaeda.
Masood drove a car through a crowd of pedestrians on Westminster Bridge, killing three and injuring about 50, then ran through the gates of parliament and fatally stabbed a police officer, before he was shot dead by police.
Neil Basu, the senior national coordinator for UK counter-terrorism policing, said there was no evidence that Masood had been radicalised in prison in 2003 and it was pure speculation to suggest that had happened.
Masood, 52, a British citizen, had several previous convictions for offences such as grievous bodily harm, possession of a knife and public order offences. He had not been convicted of any terrorism offence.
"His attack method appears to be based on low sophistication, low tech, low cost techniques copied from other attacks, and echo the rhetoric of IS (Daesh) leaders in terms of methodology and attacking police and civilians, but at this stage I have no evidence he discussed this with others," Basu said in a statement.
There had been speculation in media that Masood sent encrypted messages right before the attack.
Masood was born Adrian Russell Ajao and on Monday his mother Janet Ajao issued a statement saying she was "shocked, saddened and numbed" by his actions.