The London Times quotes an MI5 report.

Al-Qaeda leaders in Iraq are planning the first “large-scale” terrorist attacks on Britain and other western targets with the help of supporters in Iran, according to a leaked intelligence report.

Spy chiefs warn that one operative had said he was planning an attack on “a par with Hiroshima and Nagasaki” in an attempt to “shake the Roman throne”, a reference to the West.

Another plot could be timed to coincide with Tony Blair stepping down as prime minister, an event described by Al-Qaeda planners as a “change in the head of the company”.

The report, produced earlier this month and seen by The Sunday Times, appears to provide evidence that Al-Qaeda is active in Iran and has ambitions far beyond the improvised attacks it has been waging against British and American soldiers in Iraq.

There is no evidence of a formal relationship between Al-Qaeda, a Sunni group, and the Shi’ite regime of President Mah-moud Ahmadinejad, but experts suggest that Iran’s leaders may be turning a blind eye to the terrorist organisation’s activities.

The intelligence report also makes it clear that senior Al-Qaeda figures in the region have been in recent contact with operatives in Britain.

It follows revelations last year that up to 150 Britons had travelled to Iraq to fight as part of Al-Qaeda’s “foreign legion”. A number are thought to have returned to the UK, after receiving terrorist training, to form sleeper cells.

The report was compiled by the Joint Terrorism Analysis Centre (JTAC) – based at MI5’s London headquarters – and provides a quarterly review of the international terror threat to Britain. It draws a distinction between Osama Bin Laden and Al-Qaeda’s core leadership, who are thought to be hiding on the Afghan-Pakistan border, and affiliated organisations elsewhere.

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