The diplomatic row over Julian Assange’s extradition deepened on Saturday after a police officer unwittingly revealed a secret plan to seize the WikiLeaks chief “under all circumstances’’ if he stepped out of the Ecuadorian embassy here.

The officer, posted outside the embassy, was photographed with a handwritten “brief” that said Mr. Assange was to be arrested even if he left the embassy in a vehicle that had diplomatic immunity.

He is stuck in the embassy since taking refuge there two months ago to avoid extradition to Sweden over sexual assault allegations. The note marked “restricted” and titled, “EQ Embassy brief — summary of current position re Assange,” says: “Action required — Assange to be arrested under all circumstances. He comes out with dip. immun, as dip. bag (right to life) in dip. Vehicle — ARRESTED.”

An embarrassed Scotland Yard insisted that “under no circumstances will an arrest be made in breach of diplomatic immunity.” “Our object is to arrest Mr Assange for breach of bail,” it said.

The document, only partially visible and mostly illegible, warns of the “possibility of distraction” Mr. Assange’s supporters might try to create to help him escape.

Referring to an unknown agency “SS 10” giving “additional support” in carrying out the operation, it says: “Discuss possibilities of distraction SS10 to liaise ... provide additional support.”

There is also a reference to Scotland Yard’s counter-terrorism command “S020.” Most of the document, written on a ruled office sheet, is obscured by the officer’s hand.

Mr. Assange was granted asylum by Ecuador last week but Britain says it will not allow him safe passage to leave the embassy insisting that it is under “obligation” to extradite him as he has exhausted all options.

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