The son of extradited Islamist cleric Abu Hamza has been sentenced to 11 years in a young offenders' institution for his part in a 'well planned and professionally-executed armed robbery' on a Norfolk jewellers.

The raid at Francis Wain, in King's Lynn, during which almost �70,000 worth of gems were stolen, happened shortly before 10am on January 31 and involved four men.

Hamza's son, Imran Mostafa, 20, from Deverills Way, Slough, had pleaded not guilty to robbery and possessing a firearm with an indictable offence.

But he and Jonathon Abdul, 18, of Fulham High Street, London, appeared at Norwich Crown Court yesterday to be sentenced after being found guilty in August.

Mostafa was sentenced to 11 years for robbery and four years, to run concurrently, for the firearm offence while Abdul was sentenced to 11 years in a young offenders' institution for robbery and four years, also to run concurrently, for the firearm offence.

Two other defendants, Ossama Hamed, 19, of Fulham, and Ahmed Ahmed, 20, of Enfield, who had previously pleaded guilty to the same charges, were also sentenced.

Hamed was sentenced to eight years and three months in a young offenders' institution for robbery and three years, to run concurrently, for the firearm offence, while Ahmed was sentenced to seven years and four months in a young offenders institution and two years eight months, to run concurrently, for the firearms offence.

Judge Peter Jacobs described it as a 'well planned and professionally executed armed robbery' which would have been 'terrifying' for staff and members of the public during which jewellery worth �68,583 was stolen.

He said: 'It was a terrifying experience for four women of varying ages who were simply working in a shop in a small provincial town.'

He added: 'Your attitude was a totally callous and uncaring one towards those four totally decent and innocent women.'

The court was told Mostafa, 20, became involved in the offence after having been isolated from society in his childhood and youth as parents warned their children to stay away from him.

Roderick Price, for Mostafa who only had two cautions and no previous convictions, said he led a rather 'unusual life' in adding that attempts to socialise outside his home 'often met with failure because of who his father is'.

He said: 'What he found was he became more and more isolated and socialising confined to his family.'

He added: 'Children would be told by their parents not to play with him. How he dealt with this was to immerse himself on his studies.'

Mr Price described Mostafa as clearly 'a very lonely young man'.

The court heard Mostafa had a good relationship with his father up until he was imprisoned, when Mostafa was 11. From 16 he started taking cannabis and tried to break away from the family and spent a year away studying for his A Levels.

He went to university on the South Bank to study civil engineering but found it very difficult to form relationships with other students as he was 'shunned' when they found out who he was.

Mr Price said that in prison, as in life, Mostafa has also found himself segregated on a unit because of his father.

He added Mostafa knows he will 'never see his father again' after he was extradited and was 'extremely upset'.

A contempt of court order had been out in place during the trial to prevent the media identifying Mostafa as Hamza's son but was lifted by Judge Peter Jacobs after the verdict was announced.

Hamza last month pleaded not guilty to terror charges in a New York court following his extradition from the UK.

He denies charges that he conspired with US nationals to set up a terrorist training camp in the state of Oregon.

He will stand trial next August and will also face charges of abducting tourists in Yemen.

Ian James, prosecuting, said: 'You had a situation where female employees were compelled to cower behind a counter.

'In addition to producing a firearm the robbers used a sledgehammer and another tool to break display cabinets. This was a very violent intrusion and it must have been absolutely terrifying for those involved.'

Nicholas Wells, for Hamed, said his client fully accepted committing the offence and was remorseful.

He added he was a good student who does recognise the consequences of his actions in other people.

David Bird, for Abdul, who could not be identified during the trial as he was thought to be 17, said his client, even now, could not 100pc say when he was born. He said that was symbolic of the 'turmoil that's gone throughout his life.'

Abdul has lived in this country but also in Italy and Eritrea before coming to this country aged 11. He said he is himself coming to terms with what he's done and, 'in his own words' said 'Oh my days, what have I got involved in?'.

Stephen Spence, for Ahmed, said his client pleaded guilty at a time when he was entitled to maximum credit.

He said it was his first offence of violence and added he did not think through the consequences of his actions but was remorseful.

Speaking after the case, Detective Sergeant Matt Stewart said he was pleased with the result which reflected the serious and violent nature of the offence.

He said: 'It has had an impact on members of staff in the shop. It was extremely frightening and will take a long time to come to terms with but also for members of the public outside.'

Aseem Taj, of Hanson Young Solicitors, also issued a statement outside court on behalf of Mostafa. It said: 'I sincerely apologise to the victims of this terrifying incident and it deeply upsets me to hear how they have been affected by this. I pray that the almighty blesses them and their family with abundance of happiness today and for years to come.

'However I feel that this is a plot against my father, myself and my family. They locked me up for something I did not do, all because of the conspiracy against my father and his beliefs.'