Mayor Ken Livingstone has backtracked on his gaffe that he was "happy" for the terrorist son of hook-handed cleric Abu Hamza to work on the Tube.

Mohammed Kamel Mostafa, 25, had a security pass for restricted Underground areas - even though he had spent three years in a Yemen jail for plotting to blow up British and US targets.

His father is serving seven years for inciting murder and racial hatred at mosques in London.

Still, the London mayor initially said Mostafa could work for the Tube as he had not committed a crime in Britain.

"Has he broken any law here in Britain? The answer is no and we are happy to have him working for us," Mr Livingstone said at his press conference on Tuesday morning.

"No one's son should be blamed for what their parents do. All we ask is that they respect the law of the land and do not hurt anyone."

But later in the day, the mayor sent out a press statement saying the opposite.

"Mr Mostafa has convictions in Yemen. These must be taken into account.

"They should have been brought to light by those doing the security checks, the failure to do so must be investigated.

"As he failed to declare these to the subcontractor they are correct to dismiss him."

In a subsequent clarification, the mayor added that he was not aware of Mostafa's convictions at the time of his press conference that morning.

"It is clear that anyone who has been involved in terrorism in any form cannot be employed on the London Underground," Mr Livingstone said.

Mostafa worked nights and weekends as a labourer for an unnamed contractor of the maintenance firm Tube Lines. He has since left the job.

The Sun newspaper claimed Mostafa was sacked after colleagues discovered his identity. A Tube Lines spokesman declined to say why he departed.

It is thought the contactor had checked whether Mostafa had a criminal record in the UK, but not abroad - as that is not legally required.

But Andrew Dismore, Labour MP for Hendon, said: "Terrorism is an international crime.

"If somebody has a conviction for terrorism anywhere in the world, that should be a bar on them working in certain jobs.

"Bearing in mind what happened on 7/7, (Mostafa) should not have been working on the Underground."

On July 7 last year, four suicide bombers killed 52 innocent people in attacks on three Tube trains and a London bus.

John Taylor, who lost his 24-year-old daughter Carrie in the blast at Aldgate station, told The Sun: "This man is a convicted terrorist and he has been allowed access to some of the most sensitive parts of the Tube."

Shadow home secretary David Davis said: "Anyone convicted of terrorism anywhere in the world should not be allowed access to our public transport infrastructure."

A spokesman for London Underground said that it was down to the subcontractor who employed Mostafa to ensure that employees passed security checks.

He said: "The question of whether the checks were tight enough is a matter for the Government to address.

"We don't do criminal checks on every single individual who comes on to London Underground."