Fears have been raised about online extremism a year after the death of soldier Lee Rigby in Woolwich, as deadly jihadist material remains widely available online.

The young soldier was mown down in a car and hacked to death on May 22 last year by Muslim fanatics Michael Adebolajo and Michael Adebowale, prompting a Government task force to propose greater powers to block access to extremist websites.

Material from US-born radical Anwar al-Awlaki was seized from both men's houses, and is available on YouTube, something highlighted by MP Keith Vaz last year.

Today he called for renewed efforts to combat the murderous material with schemes to spread more moderate ideas and stop Muslims falling into the clutches of radicals.

Experts say the internet is giving fanatics much wider opportunities to radicalise worshippers, having migrated from more traditional means of preaching in person.

Mr Vaz, who is chairman of the Home Affairs Select Committee, said: "It is vital that horrific events such as these never happen again.

The committee recommended as part of its inquiry into counter-terrorism that more should be done to tackle online extremism.

"Internet-based and peer led counter-extremism projects hold the key. We must engage with the communities and grow counter messages organically in the same way extremist messages are expounded.

"Gaining justice for Lee Rigby does not only mean sending those who killed him to jail but also doing all we can to prevent similar attacks in the future."

Terrorist groups like al-Shabaab regularly post recruitment videos online, and one recent clip featured a jihadi performing a rap, trying to encourage fighters from English-speaking countries to fly to Somalia and join their battle group.

Tariq Abbasi, director of Greenwich Islamic Centre, also known as Woolwich mosque, said: "There was a time when the extremist groups were using Islamic centres and Mosques to preach their ideology, unfortunately, now they have wider choices at their disposal with wider geographical access to vulnerable people through internet.

"Therefore, it is difficult to handle and control."

Peter Neumann, professor of security studies at the Department of War Studies, King's College London, agreed that counter arguments should be made available online to offer more of a debate and an alternative view for those seeking out extremist material.

"The internet has replaced the physical infrastructure," he said.

"Some 15 years ago, for radical preachers, it was very easy for people to be on the ground, to that extent the internet has replaced that.

"It is now possible for people to access extremist material, to socialise with other people, to find other people.

"What the internet does for ordinary people, it does the same for extremists - it helps them find other people, to socialise with other people.

"But that doesn't mean we should shut down the internet or take a punitive approach to online material."

Mr Neumann, who is director of the International Centre for the Study of Radicalisation that he founded in 2008, warned that a Woolwich-style attack could happen again.

He said: "It doesn't require a lot of planning, it doesn't require a real weapon, you can do it in the spur of the moment."

Radical fighters in countries like Syria are already using internet video calls to recruit would-be jihadis in the UK and other Western nations, and experts have warned this will become more common.

Senior research fellow at the Royal United Services Institute Raffaello Pantucci said: "Groups like al Shabaab and al Qaida are putting clearly targeted messages online, and from Syria fighters can talk to brothers back here and recruit them.

"We've been going in that direction for a while, but it will become increasingly standard.

"There are all these different media though which you can communicate, and it makes it easier for me sitting here to communicate with someone and find out who I need to meet with."

He said that it is "very difficult to pin down" many cases where the internet has been the sole reason that a Muslim has become radicalised, but he said the internet is "an accelerator" for those beliefs.

Renewed efforts to tackle extremist material were unveiled at the end of last year by the task force set up in the wake of Fusilier Rigby's murder, with proposals for extended powers to block access to jihadi websites hosted abroad.

Earlier this year, the Home Office also confirmed that British officials had been given special "super flagger" powers by Google to allow them to have material posted on YouTube deemed to be a threat to national security instantly reviewed.