Iran twisted the knife in the hostage crisis last night, releasing a letter said to be from the captured servicewoman Faye Turney in which she called for British troops to be withdrawn from Iraq.

The letter, in which Tehran appeared to be using the hostages to try to dictate British foreign policy, was apparently designed to heap humiliation on Tony Blair.

Its release came minutes after the Prime Minister had said that he would not be drawn into any “tit for tat” deal to secure the release of the 15 servicemen, and took the stand-off into increasingly unpredictable territory. A livid Mr Blair denounced the new letter, the second to be released by the Britons’ captors. “It is cruel and callous to do this to somebody in this position and playing this kind of game — it is a disgrace,” said the Prime Minister’s spokesman.

According to a text of the letter, released by the Iranian Embassy in London, the 26-year-old mother wrote: “Isn’t it time for us to start withdrawing our forces from Iraq and let them determine their own future?”

Iran had earlier reneged on its promise to release Leading Seaman Turney and gone back on a pledge to let British diplomats visit the detainees, who have been held in secret locations since Friday. As the standoff deteriorated, Iran threatened to put the 15 on trial and claimed it had satellite evidence that they breached its borders six times.

Last night, however, Iran again dangled the possibility that Leading Seaman Turney might be freed soon. Asked by Recep Tayyip Erdogan, the Turkish Prime Minister, to free the only woman among the British captives, President Ahmadinejad promised to study the request “in a positive manner”, according to Iranian television. The UN Security Council, voicing “grave concern”, meanwhile called on Iran to allow consular access to the detained British naval personnel and urged “an early resolution of this problem, including the release of the 15”.

Britain originally asked for a tougher three-sentence statement to “deplore” the detention of the British personnel and “support calls” for their immediate release, but this was blocked by Russia and several other members.

“We will not be able to accept a call for the immediate release of the 15 UK naval personnel,” Vitaly Churkin, Russian’s UN envoy, declared during the debate.

The final two-sentence statement was read to the press outside the Security Council chamber, making it weaker than a formal declaration.

The latest letter from Leading Seaman Turney, dated Tuesday, was addressed to “representatives of the House of Commons”. It said: “Unfortunately during the course of our mission we entered into Iranian waters.

“Even through our wrongdoing they have still treated us well and humanely, which I am and always will be eternally grateful for. I ask the representatives of the House of Commons, after the Government have promised that this type of incident would not happen again, why have they let this occur, and why has the Government not been questioned over this?” A written and video confession by Leading Seaman Turney had previously been shown on Iranian TV, increasing concerns that she was being pressurised into making propaganda statements.

Iranian TV last night imitated the MoD briefing that launched Mr Blair’s offensive. A Tehran military officer was shown in front of a map of the Gulf, holding up an electronic positioning device seized from the Britons and pointing at numerous spots where he claimed they had trespassed.

Iran appeared to be punishing Mr Blair for a diplomatic offensive built around claims that Iranians deliberately lied when saying the Royal Navy had violated their waters.

GULF STANDOFF

Britain’s case
The Royal Navy were boarding a ship in Iraqi waters when Iranian patrol vessels ambushed them

Evidence provided
On Sunday, a helicopter flew over a vessel anchored in the Gulf and photographed its position recorded by satellite device. This showed a point 1.7 nautical miles inside Iraqi waters. Britain says that the ambush happened here

Evidence missing
The boarding team had communications equipment broadcasting their position back to HMS Cornwall. The Ministry of Defence has declined to provide computer printouts.

Possible holes
— The timing has changed. On Friday the MoD said that it happened at 10.30am. By Wednesday, it said that communications went dead at 9.10am.
— The boarded vessel has changed. Early reports described it as a dhow or Arab sailing craft. The MoD says it was a cargo ship.
— The Iranians have shown footage of the boarding team getting off a dhow
— Iraq at first backed Iran. Brigadier-General Hakim Jassim, in charge of Iraq’s territorial waters, said on Saturday: “We were informed by Iraqi fishermen that there were British gunboats in an area that is out of Iraqi control.” By Wednesday, Iraq backed Britain.
— The MoD says that debriefing of the helicopter crew indicates that the team was ambushed leaving the merchant vessel. But the helicopter had flown back to the Cornwall

Iran’s case
The British boats entered Iranian waters six times.

Evidence provided
Televised and written confessions by Faye Turney, a boat driver

Evidence missing
Although Iran claims satellite equipment on the seized boats proves the British entered their waters, data from the machine has yet to be produced.

Possible holes
— Leading Seaman Turney’s admissions are unspecific, stilted and use language reminiscent of brainwashing or coercion
— Iranian diplomats originally provided coordinates to Britain claiming to prove the Royal Navy entered their waters. After Britain pointed out the compass references showed a spot in the Iraq’s sphere, Iran changed the reference
— An Iraqi fisherman insisted to Reuters that the British had been searching a ship in Iraqi waters

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