Internet service providers should do more to fight violent extremism in Britain by clamping down on its online havens, MPs said Monday in a report that also urged broad vigilance on the threat from the far right.

The web is a more significant vehicle for promoting radicalism than prisons, universities or places of worship, and is involved in almost all cases of violent extremism, the Home Affairs Committee said in their report "The Roots of Violent Radicalisation".

Law enforcement agencies can already order illegal material to be removed from the Internet, but "service providers themselves should be more active in monitoring the material they host," the report said.

The MPs recommended that the government work with Internet service providers (ISPs) to develop a code of practice on removing violent extremist material, but acknowledged international co-operation would also be needed.

ISPs told the committee it would be "impractical" for them to actively monitor material, the report said, citing the sheer volume of online content and implications for freedom of expression.

But security expert Peter Neumann, of King's College London, told the committee: "This is not about freedom of speech. All these websites, whether it is YouTube or Facebook, have their own rules... They are very effective in removing sexual content or copyright content.

"Why can they not be equally effective at removing, for example, extremist Islamist or extremist right-wing content?"

The report comes after four British Islamists admitted to plotting to blow up the London Stock Exchange in 2010, having acquired al-Qaeda materials online. They are due to be sentenced this week.

However, terrorism experts told the committee that support for violent Islamist extremism in Britain was declining, reflected in a gradual drop in the conviction rate from 51 terrorism-related convictions in 2006/07 to four in 2010/2011.

The report said that disaffected young Muslims should be targeted with affirmations that"the British state is not antithetical to Islam" and the government's "Prevent" strategy, which aims to fight extremist ideology, should be renamed "Engage".

It also urged a clearer strategy against violence from the far right in the wake of the terror attacks in Norway by white supremacist Anders Breivik, which killed 77 people.

The MPs received "persuasive evidence about the potential threat from extreme far-right terrorism" although this consists "mostly of solitary, disaffected individuals rather than organised terrorist units", they said.

Britain was attacked by home-grown Islamists in 2005, with four bombs on London public transport killing 52 people in addition to the attackers.

It has also experienced clashes between Islamist and anti-Muslim protesters in recent years, but on a small scale.