A British judge sentenced an Arab man to 11 years in prison for keeping a cache of explosives for the Palestine Liberation Organization in his home. Judge Christopher French of Old Bailey's Central Criminal Court told Ismael Sowan on Thursday that the sentence was the very least he could give for his ``extremely grave offences.'' Sowan, 28, was convicted Wednesday of storing explosives, rifles and grenades in his home in the eastern port of Hull. In announcing the sentence Thursday, the judge said, ``we were reminded ... only yesterday of the appalling use to which these materials can be put.'' The reference was to a bombing in Northern Ireland that killed six soldiers and wounded 10 civilians Wednesday. Sowan was arrested last August when police were investigating the shooting death of an Arab cartoonist, Ali Naji Awad Al-Adhami. Although he was arrested in Hull, Sowan's trial was held in London at the Old Bailey court because cases involving security and terrorism usually are tried there and because Scotland Yard had participated in the investigation. Sowan testified that the weapons found in locked suitcases in his bathroom belonged to Abder Mustapha, a known PLO guerrilla suspected of organizing Al-Adhami's murder. Police said that Mustapha fled to the Middle East after Al-Adhami was shot in the head. Sowan, a university research assistant, is not a suspect in that crime, although he was a friend and associate of Mustapha. After his arrest, Sowan claimed to be funneling information about Mustapha to the Israeli secret service Mossad. Officials at the Israeli Embassy in London confirmed that Sowan was in contact with them, and that he had told them that he had Mustapha's weapons. British police and intelligence agencies said they did not know about the spying operation and did not receive information from Mossad about the weapons cache during the investigation. David Cocks, Sowan's defense attorney, said the Israeli factor made his client innocent.