As evidence, they point to the fact that Israeli diplomats were deported from the UK after the incident.
As usual, they aren't telling the whole truth. All evidence indicates that Naji al-Ali was killed by the PLO. Britain never said Israel was behind the assassination - they were upset that the Mossad knew that the PLO was going to assassinate al-Ali and did not inform British intelligence.
Believe it or not, Electronic Intifada has a reasonable description of what happened:
On Wednesday July 22 1987 at five in the afternoon, Palestinian cartoonist Naji Al-Ali parked his car in southwest London, and walked a few meters towards the offices of the Kuwaiti newspaper Al-Qabas where he worked. He was shot in the head by a gunman, dressed in a denim jacket, who walked calmly away down Draycott, near Sloane Square and vanished.More from The Independent:
After five weeks in a coma on a life support machine at St Stephen’s hospital and the neurosurgical department of Charing Cross hospital in London, Naji al-Ali died at 5am on Saturday, August 30, 1987 at the age of 49.
A friend of Naji al-Ali was quoted saying that he had been warned his life was in danger in a telephone call from a senior member of the PLO in Tunis. The telephone call, two weeks before the murder, came after the publication of a cartoon attacking a female friend of PLO leader Yasser Arafat. “The cartoon was famous in the Arab community,” the friend said. The caller said: “You must correct your attitude.”
“Don’t say anything against the honest people, otherwise we will have business to sort you out,” the caller continued. Naji al-Ali ignored the warning and published a cartoon lampooning Arafat and his henchmen on 24 June.
Ten months after Naji al-Ali was shot, Scotland Yard arrested a Palestinian student who turned out to be a Mossad agent. Under interrogation, the Jerusalem-born man, Ismail Suwan, said that his superiors in Tel Aviv had been briefed well in advance of the plot to kill the cartoonist.
By refusing to pass on the relevant information to their British counterparts, Mossad earned the displeasure of Britain, which retaliated by expelling two Israeli diplomats from London.
THE BRITISH and Israeli secret services failed to prevent terrorist attacks, including "hits" by Palestinians on the streets of London, because of inter-agency feuds, according to newly published evidence:The person arrested in connection with the case, Ishmail Hassan Sowan, admitted to being a double agent for the Mossad but as a PLO employee he had amassed a huge stash of weapons for PLO terror attacks across Europe.
The poor relations resulted in a number of fiascoes:
The British knew of the plan in 1982 to assassinate Shlomo Argov, the Israeli ambassador to London, but the Israelis were not warned.
The Israelis knew the Palestinian satirical cartoonist Nagy el-Ali el-Adami was to be assassinated in London in 1987 by his countrymen. The British were not told because Israel did not want to expose its double agents in the PLO's London-based cells.
The best description of how much Arafat hated Naji al-Ali comes, unfortunately, from an ancient Angelfire page that supported al-Ali's work:
On July of 1987, the London Observer published a caricature with the title: "The Deadly Joke That Cost a Cartoonist His Life".
Starting from the right side of the caricature,
Arab peasant (A) says: "Do you know Rashida Mahran?"
Bourgeoisie Arab (B) replies: "No."
A says: "Have you ever heard of her?"
B replies: "No."
A says: "You never met her and never heard of her! Then how did you become a member of the Public Institute of Palestinian writers and journalists? ... Who is backing you in this Organization [PLO] you son of a bitch?"
Two days before his assassination, Naji Al-Ali was interviewed by Al-Azminah Al-Arabiya (Arab Times) Magazine, which represented the opposition in the United Arab Emirates, produced by Mr. Ghanim Ghabbash (also killed later on). The interview was published in the 170th issue on August 15, 1987. In that article, it was mentioned that Chairman of the PLO, Yasser Arafat, had once stood before Abdallah Al-Salim highschool in Kuwait, 1975, to present a speech to the students. In that Speech, Arafat said: "Who is this Naji Al-Ali? Tell him if he doesn't stop drawing cartoons I will put his fingers in acid!"
Ghanem Ghabbash, who himself interviewed Naji, reported Naji's words: "Do you know this Rashida Mahran? Don't mistaken her for one of the freedom fighters. Rashida Mahran is a very important lady who rides Arafat's private jet and lives in a castle in Tunisia, where she has great influence on the organization (i.e. PLO) and its institutions. I made a cartoon about her, and after that I have received dozens of threats, blessings, and sympathy. Can you imagine that someone contacted me on behalf of Abu Iyad [one of the major leftist figures of PLO, who was killed later on by Israelis], and told me how delighted he was with the cartoon, and said that I have done something [great] that no other top official in the organization could do. But he also said that I have crossed the red lines and that he was worried about me and asked me to take care of myself. So I told him: My brother, if I'd take care of myself, I wouldn't have enough time to take care of the rest of you."
It is ironic, but not unexpected, that a cartoonist that was assassinated quite directly by the PLO for his political cartoons is now being used as evidence that Israel kills cartoonists. Perhaps the Mossad could have saved his life but the decision and implementation of the murder was by the PLO.
The story blaming Israel for al-Ali's death is just as bogus as the false story that Israel jailed Mohammad Saba’aneh because of his cartoons.