The Home Office missed several chances to deport him, and he was granted British citizenship, even though he had married bigamously, made bogus claims about fathering a child here and been arrested as an illegal immigrant.

The disclosure in The Times today is likely to intensify demands by MPs for an inquiry into why no action was taken against the Egyptian-born extremist before his conviction at the Old Bailey this year.

A new investigation has revealed how the former Finsbury Park mosque imam falsely claimed on a birth certificate in October 1980 that he was the father of a daughter born to his first wife, Valerie Traverso.

Earlier the same year the couple had married bigamously, barely ten months after Abu Hamza arrived in Britain to dodge national service in Egypt. Documents seen by The Times show that Mrs Traverso had not divorced Michael Macias, her first husband, when she married Abu Hamza at Westminster Register Office in May 1980. Ms Traverso also told The Times she was already pregnant when they met. She insists that she had not realised the couple were committing bigamy.

Separated from her first husband when she met and married Abu Hamza, she describes it as “a mix-up, a simple confusion”.

Details of her daughter’s birth certificate are published in a new book The Suicide Factory, which is serialised in The Times today. They show that Abu Hamza — then using his real name of Mostafa Kamel Mostafa — claimed to be her father. The book also reveals that four days after the child was born, Abu Hamza instructed his lawyers to write to the Home Office to apply for permission to remain. He was later arrested as an illegal immigrant and went on to plead guilty at a magistrates’ court to overstaying his visitor’s visa. He was given a conditional discharge, but, had his immigration status been investigated, he could have been deported. Instead, six months later, he was given permission to remain.

Abu Hamza is now in Belmarsh top security prison in South London after being sentenced to seven years for incitement to murder and racial hatred. The Government is trying to strip him of his British citizenship, and America wants to extradite him on terrorism charges.

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