Iran has said it will release the eighth of nine British embassy employees detained in Tehran, Foreign Secretary David Miliband has revealed.

But he vowed to continue to fight for the freedom of the remaining detainee who is facing a possible trial on charges Mr Miliband insisted had "absolutely no substance".

The staff were arrested last weekend amid rapidly-deteriorating relations with Iran since the disputed re-election of president Mahmoud Ahmadinejad and the street protests that followed.

"I spoke to our ambassador on our daily call last night and the good news is that he was told by the deputy foreign minister that the eighth person would indeed be released today, that the papers have been signed and that there would not be a court process or charges.

"That leaves one more in custody and all of our efforts are now directed towards getting that person out," he said.

The embassy's chief political analyst, Hossein Rassam, an Iranian, was identified by his lawyer as the individual who remained in detention facing a charge of "acting against national security".

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