Security officials are currently working to find out if Khalid Masood was radicalised during the time he spent in prison for slashing the face of a pub landlord.
Muslim converts are four times more likely to commit acts of terrorism and related offences than people born into the religion, a study by the Henry Jackson society claims.
And experts are concerned by the fast pace of prison radicalisation, with many forming Islamist gangs while behind bars.
Muslim converts are four times more likely to commit acts of terrorism
Raffia Hayat of the Ahmadiyya Muslim association has warned of attempts by jailed extremists to recruit violent criminals into radical groups so they can carry out attacks on the public once released.
Mr Hayat added: “It is worrying and this is something the Government should take seriously and find ways to not allow that to happen in our prisons in the UK."
Steve Gillan, general secretary of the Prison Officers Association, claimed inmates often aligned themselves with radicalised gangs for protection before taking on their twisted ideologies.
How the front pages of newspapers reported the London terror attack Thu, March 23, 2017
Media across Europe, to the USA, the Middle East have paid tribute to the victims
1 of 20
Steve Gillan claimed inmates often align themselves with radicalised gangs
He told the Mirror: "There is a gang culture where prisoners are being bullied into these groups often as a way of protecting themselves.
"Muslims represent the fastest growing faith group in our prisons but many of them aren't practicing after they leave, you have to ask why that is.
Get Quotes on Home Insurance
"Although prison officers can spot these problems there aren't enough staff numbers and they don't have the training to properly de-radicalise these people.
"It means you're basically warehousing people in an environment where they are becoming extremely dangerous to society and not dealing with the problem before they're sent back out onto the streets."
Masood is one of many converts to attempt acts of horrific terror in the UK
Experts are concerned by the fast pace of prison radicalisation
Masood is one of many converts to attempt acts of horrific terror in the UK.
In 2005, convert Germaine Lindsay took part in the 7/7 bombings, while Michael Adebolajo and Michael Adebowale converted from Christianity to Islam before killing Fusilier Lee Rigby in 2013.
Jahan Mahmood, a former government adviser on radicalisation, said it was “pretty undeniable” there was an issue in prisons which needed to be addressed.
He added: “At this moment, we have no conclusive picture of Masood's radicalisation so to speak – was it in prison, was it after prison, was it because of people that he may have known from prison?”