According to the report, British authorities are also concerned about security searches carried out on British officials attending a terrorism conference in Israel last September.
MI6 believe that Britons flying to Israel have been targeted for months and their documents have been cloned, the newspaper said, adding that the Foreign Office held top level talks last week on whether to issue a warning against travelling with certain airlines.
The forging method was already revealed last week in a statement made by the British government to the parliament after the use of British citizens' identities in the Dubai assassination was revealed. According to the statement, 12 passports used by the assassins were cloned in different airports while the British nationals were on their way to Israel. They were taken away for "examinations" which lasted 20 minutes each.
In addition to the investigation into the falsification of British passports, the United Kingdom authorities are also checking whether Israeli intelligence elements took advantage of a visit to Israel by British security officials in order to clone their passports.
British police sources said the officials had undergone strict security checks upon arriving in Israel.
"It was said to be routine but the searches did not apply to all nations," a source told the newspaper. "There is now a real concern that some of these high-ranking officers and officials have also had documents cloned."
The UK expressed its discontent after Dubai authorities revealed that British identities were used in the assassination and launched an investigation into the matter. One of the moves taken against Israel was the decision to expel an Israeli diplomat serving in the kingdom, which was said to be the Mossad representative in London.
It was also reported that Israel would not be allowed to replace its Mossad representative in London should it not provide Britain with a public assurance that UK citizens' passports will never be used again for secret operations.
British Foreign Secretary David Miliband told lawmakers last week that Israel's actions had put British nationals at risk and showed a "profound disregard" for Britain's sovereignty. He said the fact that Israel is a longtime ally with close business, personal and political ties to Britain "adds insult to injury" in this case.
Miliband noted that a thorough British investigation concluded that Israel was behind the forging of British passports used by the alleged assassins in Dubai.