Islamic converts and 'born-again Muslims' are particularly vulnerable to radicalisation because of their 'vacuum of knowledge', a new report has found.

Research has found that new converts, although mostly peaceful, are disproportionately over-represented in terror groups including ISIS. Lee Rigby's killers and the Westminster attack Khalid Masood are examples of recent converts who have committed atrocities, the study pointed out.

'When taken together with other aggravating factors such as possession of a criminal record, paternal absence, and exposure to the messages of radical preachers, the process of conversion can indicate a vulnerability to extremism,' the report by the Henry Jackson Society think-tank said.

'Converts are often more malleable and vulnerable to radical rhetoric, often combining enthusiasm to change the world with a vacuum of knowledge about different interpretations of Islam.'

The evidence adds to the theory of a 'crime-terror nexus' where young people involved in gangs and petty crime are lured into Islamist networks with the promise of salvation and purpose.

Dr Julia Rushchenko, an associate fellow at the HJS Centre for the Response to Terrorism and Radicalisation, said the 'pernicious ideology' of radical Islam 'has proven capable of luring a wide range of individuals from across Europe'.

She said: 'Policy-makers and practitioners must be alert to this specific but understudied danger, if they are to counter extremism effectively.'

It came as the UK's 'terror tsar' Max Hill QC warned that new terror laws would 'criminalise thought' and said it was 'quite wrong' to punish 'though without action'.

He was speaking to the human rights group Justice on Tuesday, according to the BBC, after the home secretary Amber Rudd announced plans to increase prison sentences for those guilty of viewing extremist content online.

'Whilst we can all agree that there should be nowhere for real terrorists to hide, we should also agree that legislating in the name of terrorism when the targeted activity is not actually terrorism would be quite wrong,' he said.

'We do not, and should not criminalise thought without action or preparation for action.

'Thought with steps towards action can be terrorism. Thought without action or preparation for action may be extremism, but it is not terrorism.'