Iran further raised the stakes in the diplomatic stand-off with Britain tonight by releasing a second letter said to have been written by Royal Navy rating Faye Turney.

In the the hand-written note, released by the Iranians to Sky News, Leading Seaman Turney is said to have called for the withdrawal from British troops from Iraq.

There was no immediate response from the Foreign Office, however it is likely to raise concerns fresh concerns that it was written under some form of duress.

The letter, dated March 27, was addressed to “representatives of the House of Commons” and states: “Isn’t it time for us to start withdrawing our forces from Iraq and let them determine their own future?"

Iranian television also aired new footage apparently showing the capture of 15 Royal Navy personnel.

In the five-second clip of film gunshots can be heard and a helicopter is shown hovering above inflatable boats in choppy seas.

The video, shown on Iranian state television, then switches to an Iranian military official who outlines the Iranian position that the British vessels had strayed into their national waters.

The letter and footage was released as Britain continued attempts to finalise a UN Security Council resolution condemning the seizure, calling for the captives' immediate release and declaring they was taken during a routine patrol in Iraqi waters under a UN mandate.

The UK has called for the resolution after freezing all bilateral ties with Iran except for contacts directly related to the hostage crisis.

After accusing Britain of making a "fuss", Iran this afternoon responded by going back on its promise that Leading Seaman Turney would be released, claiming that she would now remain in captivity.

The crisis, which has contributed to oil prices surging to a six-month high of over $65 a barrel, was discussed between Hoshyar Zebari, the Iraqi Foreign Minister, and his Iranian counterpart at the Arab League Summit in Riyadh. Mr Zebari said that that he had demanded that the sailors be freed.

"Our information is that they were arrested and detained in Iraqi territorial waters," he said.