Anjem Choudary, the leader of the dissolved militant group al-Muhajiroun, arrives at Bow Street Magistrates Court in London July 4, 2006. Thomson Reuters

Anjem Choudary, Britain's most high-profile Islamist preacher whose followers have been linked to numerous plots across the world, has been found guilty of inviting support for Islamic State.

Choudary, 49, was convicted at London's Old Bailey court of using online lectures and messages to encourage support for the banned group which controls large parts of Syria and Iraq.

Notorious in Britain where the tabloids denounce him as a hate preacher, he is also well-known abroad, making regular TV appearances in the wake of attacks by Islamist militants to blame Western foreign policy for targeting Muslims.

"These men have stayed just within the law for many years, but there is no one within the counter terrorism world that has any doubts of the influence that they have had, the hate they have spread and the people that they have encouraged to join terrorist organizations," said Dean Haydon, head of London police's Counter Terrorism Command.

Prosecutors said that in postings on social media, Choudary and his close associate Mizanur Rahman, 33, had pledged allegiance to the "caliphate" declared by Abu Bakr al-Baghdadi and said Muslims had a duty to obey or provide support to him.

Both men, who had denied the terrorism charges and claimed the case was politically motivated, were found guilty last month but their convictions could not be reported until Tuesday for legal reasons. They are due to be sentenced in September and could face a jail sentence of up to 10 years each.

Anjem Choudrey (L) and Abu Saah, spokesmen for the controversial Islamic group Al-Muhajiroun, speak during a news conference in east London marking the third anniversary of the terror attacks on the World Trade Center, September 11, 2004. Thomson Reuters

Choudary, the former head of the now banned organization al-Muhajiroun, became infamous for praising the men responsible for the 9/11 attacks on the United States and saying he wanted to convert Buckingham Palace into a mosque.

Despite his often controversial comments and refusal to condemn attacks by Islamists such as the London 2005 bombings, Choudary has always denied any involvement in militant activity and had never been previously charged with any terrorism offence.

Rahman served two years in jail for encouraging followers to kill British and American troops in Afghanistan and Iraq during a protest in 2006.

Breeding ground for militants

Al-Muhajiroun has been regarded as a breeding ground for militants since it was founded in the late 1990s by Syrian-born Islamist cleric Omar Bakri, who was banished from Britain in 2005, and was banned under anti-terrorist laws in 2010.

Police said it was suspected of being the driving force behind the London bombings while Michael Adebolajo, one of the men who hacked to death British soldier Lee Rigby on a London street in 2013, had attended protests Choudary had organized.

Last year, the trial of a teenage Muslim convert found guilty of plotting to behead a soldier in London was told he had fallen in with al-Muhajiroun.

The group's influence is said to extend far beyond Britain. Those connected to it include Abu Hamza al-Masri, jailed for life in the United States last year for terrorism-related offences.

Michael Zehaf-Bibeau, the gunman who shot and killed a soldier in Canada's capital and then stormed parliament in 2014, followed Choudary on Twitter, although the preacher told Reuters at the time he had no links to him.

"Over and over again we have seen people on trial for the most serious offences who have attended lectures or speeches given by these men," Haydon said in a statement.

Both Choudary and Rahman say they abide by a "covenant of security" which forbids Muslims from carrying out attacks in non-Muslim lands where their lives and wellbeing are protected.

"We're living in a global community and no doubt Muslims around the world who have their eye on what's happening in Syria and Iraq or want to know about the sharia (law) will come across us at one point or another," Choudary told Reuters in 2014.

"That does not mean that we're encouraging people to carry out any acts of terrorism."