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Woolwich murder suspect Michael Adebolajo appeared in court in Kenya three years ago, suspected of leading a group of Islamists trying to join terrorists in Somalia.

He was held by police close to the Somali border with a brand of “radicalised” Muslim youths who wanted to join the notorious al-Shabaab group.

He was deported to Britain after he appeared in court in Mombasa in November 2010.

Two months earlier the head of MI5 had warned that Britons were training in Somalia and that it was “only a matter of time before we see terrorism on our streets inspired by those who are today fighting alongside al-Shabaab”.

The disclosures raise further questions about the monitoring by the security services of Adebowale, 22, and Adebolajo, 28, who, say sources, was known to MI5 but not assessed as a “threat to life”.

Last night Conservative MP and former Army colonel Patrick Mercer told the Sunday Mirror: “It is extraordinary that this individual was detained on the Kenyan border with Somalia yet our security services did not act.”

Adebolajo was arrested by Kenyan authorities in the coastal town of Lamu, before being taken to Mombasa, where he was detained. He appeared in court in November 2010 with other alleged ­Islamists. He and the others, aged from 18 to 22, were remanded by police.

A court report at the time said he was a “Nigerian who had a British passport”. Sources in the country confirmed his identity yesterday and said Adebolajo was subsequently deported. He later complained that he had been mistreated.

Adebolajo is understood to have said in court that he wanted access to legal services and to talk to the British ambassador to Kenya. He also complained that the police had told him he was a Christian, when he was a converted Muslim.

“He was very arrogant and he was restrained,” the source said. “We deported him back to the UK. When he was back in the UK he complained about us, that we tortured him. The British embassy in ­Nairobi wrote to us about the complaint, we told them that we did not torture him. I do not know if the letter arrived but that was what we wrote to them.”

According to newspaper reports at the time, the group boarded a speedboat from Lamu Island to the nearby village of Kizingitini before their arrest.

Police suspected Adebolajo of masterminding a plan for the youths to join al-Shabaab in Somalia.

The other youths who appeared with Adebolajo said they were recruited from a mosque in Mombasa by a radical imam. While in Lamu they spent time at an isolated madrassa.

Lamu, 68 miles from the Somali border, is the key crossing point to the country and a major area of operations for Kenyan security forces.

The case raises questions about why Adebolajo was not put under greater surveillance or even prosecuted after his deportation. Under the Terrorism Act 2006, it is an offence to travel overseas to commit acts of terrorism or take part in terrorist training.

Evidence from the Kenyan authorities could have been used in the UK to prosecute Adebolajo. It is alleged that Adebolajo was arrested while studying in a village in Kenya last year.

His friend Abu Nusaybah told BBC2’s Newsnight on Friday that ill-treatment in Kenya by MI5 operatives led to his radicalisation.

After refusing to answer questions Adebolajo was allegedly told that he was “not in the UK” and was then allegedly sexually assualted.

On his return, said his friend, Adebolajo was “more reclined, less talkative. He wasn’t his bubbly self.”

He is said to have turned to a lawyer to complain about harrassment by MI5. Last night it emerged that Abu Nusaybah’s real name is Ibrahim Hassan, 31, and that he is a former member of Al-Muhajiroun, a group banned in the UK in 2010.

Al-Shabaab is an al-Qaeda cell based in Somalia where it controls larges swathes of the country and has imposed its own strict form of sharia law.

Made up of around 14,500 young militant Islamists, it has declared jihad – holy war – on the “enemies of Islam” and has been blamed for kidnapping and killing aid workers.

Last night, the father of murdered London schoolboy Damilola Taylor said that he had acted as a mentor to Adebowale, known to his friends as Toby.Speaking to ITV News Richard Taylor said of Wednesday’s events: “It’s a different Toby or Michael that I was seeing. I don’t believe it was anything Islamic.”

Mr Taylor, whose 10-year-old son was killed in South London in 2000, said he had tried to help Adebowale after he was bullied at school and then became involved in drugs and gangs.

But he said that when he spoke to Adebowale two months ago, he was him that he had become a Muslim.

Mr Taylor said he had also known Adebowale’s mother, a probation officer, and that his father was a representative in the Nigerian High Commission.

It was revealed yesterday that David Cameron is planning to gag Muslim hate preachers with new powers.

The Prime Minister wants to stop extremists using schools, colleges, prisons and mosques to spread their “messages of poison”.

He will head a new Tackling Extremism and Radicalisation Task Force (TERFOR) made up of senior politicans, MI5, ploice and moderate religious leaders.

The task force will look at a number of measures including banning extremist clerics from being given a platform to incite potentially vulnerable followers to their cause.