The letter was released by the Iranian embassy in
Foreign Secretary Margaret Beckett accused
Shadow Defence Secretary Liam Fox said: "This is an abuse of the rights and dignity of our service personnel.
"The content of the letter is not credible and it represents a grotesque, cruel and counterproductive act of propaganda."
There were immediate fears Leading Seaman Turney wrote the letter under duress, with Mrs Beckett expressing "grave concerns" about the circumstances in which it was prepared.
Some language experts are already questioning the letter's validity, the suggestion being that the language used indicates the letter is an English translation of a Farsi original. And look at her signature, cowering in the bottom corner, half the size of the rest of the writing.
And Captured sailor Faye Turney was "clearly coerced" into writing a letter in which she apparently called for British troops to withdraw from
John Nichol, an ex-RAF navigator who was shot down in 1991 and held captive during the first Iraq War, said the 15 seized sailors and marines would be trying to placate their captors.
It was wrong to attempt to second guess why Leading Seaman Turney might have written the letter because she was in a "parlous situation", he added.
Mr Nichol told Sky News: "Faye was clearly coerced into making the TV broadcasts that we saw yesterday and today.
"She was clearly coerced into writing the letter, and she was clearly coerced into writing the letter that's been released this afternoon. No serviceman or woman is going to volunteer to do that sort of thing. No serviceman or woman is going to pick up a pen when captive and write to their dearly beloved MP. It's a nonsense.
I don't know what level of coercion was used, and in many ways it doesn't matter. But she was under duress when she wrote those things and said those things. The captured service personnel will be trying to keep the situation calm.”