Imran Mostafa, 20, of Deverills Way, Slough, denied robbery and possessing a firearm with intent to commit an indictable offence.
The jury at Norwich Crown Court today convicted him of both offences after more than five hours of deliberation.
Mostafa is the son of radical preacher Abu Hamza, 54, who was jailed for seven years in 2006 for soliciting to murder and inciting racial hatred, and is currently facing extradition to the US to face terrorism charges.
The jury heard that members of the shop staff at Francis Wain jewellers in Kings Lynn, Norfolk, cowered behind counters in the morning raid on January 31 as three men, wearing hooded tops to disguise their faces, burst into the store.
One man brandished a firearm and another a hammer which was used to break the display cabinets. A third stayed in a van.
They dumped the van nearby before returning to London, stopping at Gayton to dump some jewellery casing on wasteland.
Prosecutor Ian James said: "One of the robbers let off some sort of smoke bomb causing confusion, and stock was taken as loads of glass fragments went everywhere because of the way the robbery was conducted."
Civil engineering student Mostafa told the jury he was teaching Arabic and the Koran at a community centre in London at the time of the robbery.
Mostafa told the jury: " I am not a thief. I am not an armed robber."
Mostafa's parentage was previously subject to a court order and could not be disclosed; however, following the return of the jury's verdict the judge decided to overturn the order.
Jonathon Abdul, 17, from Fulham, London, who also denied the offences, was convicted alongside Mostafa.
Two others admitted the offences: Ossama Hamed, 19, of Gresswell Street, Fulham, and Ahmed Ahmed, 19, of Nags Head Road, Enfield.
All four will be sentenced at a later date.
