Internet service providers (ISPs) must do more to monitor online content and bring in a code of practice because the web plays a role in most, if not all cases of violent extremist radicalisation, a committee of lawmakers said on Monday.

The Internet was a more significant way for extremists to promote their agenda and seek recruits than prisons, universities or places of worship, parliament's Home Affairs committee said in a report.

More resources need to be directed to these threats and to preventing radicalisation through the Internet and in private spaces, committee chairman Keith Vaz said.

These are the fertile breeding grounds for terrorism.

Politicians and security officials have for years warned of the problem the Internet posed, but little has been offered as a solution, partly because of the difficulties in imposing rules without restricting freedom of speech.

Last week, prosecutors said four Islamists, who admitted plotting to bomb the London Stock Exchange, had been inspired by the online propaganda of Anwar al-Awlaki, a U.S. citizen linked to al Qaeda's Yemeni branch who was killed last year in a CIA drone strike.

Officials also say a young woman who stabbed a lawmaker in his London offices in 2010 had been radicalised solely by online material.

We suggest that the government work with Internet service providers in the UK to develop a code of conduct committing them to removing violent extremist material, the committee said in its report, titled The roots of violent extremism.

However, trade body the Internet Service Providers' Association told the committee ISPs were not best placed to determine what constituted violent extremism and said it would be impractical for them to monitor all material because of the sheer volume of content.

Last year Norman Bettison, Britain's lead police officer on the counter-radicalisation strategy known as Prevent, told Reuters the issue could only be solved through global agreement, as enforcement action could only be taken against websites in the country were they were hosted.

Two years ago, Britain launched a specialist police unit to tackle UK websites promoting extremist material, and this had received 2,025 referrals, about 10 percent of which had led to websites or web pages being taken down.

Bettison told the committee this was a pebble thrown into the world wide web ocean.

While the committee concluded support for violent Islamism was in decline, it said the British government paid only lip service to the threat from extreme far-right terrorism, which it warned posed a growing risk.

(Editing by Sophie Hares)