Iran aired the first pictures of British sailors and marines captured in the Gulf last week as London pressed for access to the 15 personnel whose detention has set off a major diplomatic crisis.
The only woman sailor was shown in the broadcast Wednesday saying they had trespassed into Iranian waters, but Britain reacted angrily to the detainees being paraded on state television and demanded their immediate release.
It was the first time the 15 had been seen since they were seized at gunpoint by Iran during what Britain said was a routine patrol of Iraqi waters in the northern Gulf.
London on Wednesday froze ties with Tehran over the crisis and protested over the footage, saying Iranian promises to release the only woman soon were insufficient.
The television showed the Britons having a meal and featured Faye Turney, 26, wearing a black headscarf and saying: "Obviously we trespassed in the waters."
"They were friendly, very hospitable, very thoughtful. Nice people," she said of her captors, who have kept them at a secret location and not allowed them any contact with British diplomats.
Britain said it was waiting to hear directly from Iranian officials following press reports that Tehran will grant access to the group.
"We await further details from the Iranian government on their undertaking to act on our request for consular access to the Royal Navy personnel," said a Foreign Office spokesman.
"We continue to press strongly for their immediate release."
Foreign Secretary Margaret Beckett said she was "very concerned" about the pictures and "any indication of pressure on or coercion of our personnel" who she said were on a routine operation in accordance with international law.
The crisis erupted at a time of high international tensions over Iran's controversial nuclear programme which the West fears could be a cover for ambitions to build atomic weapons.
Iran insists the 15 had "illegally entered" its territorial waters, but on Wednesday said that Turney would be released in one or two days.
However, a British Foreign Office spokesman said: "Obviously the release of one person, one of the military personnel and not the others, is not good enough.
Beckett on Wednesday also announced a freeze in official dealings with Iran.
"We need to focus all our bilateral efforts during this phase on the resolution of this issue," she said. "We will therefore be imposing a freeze on all other official bilateral business with Iran."
Britain also revealed evidence that it said showed the 15 were in Iraqi waters when detained.
Iran rejected this and played down Britain's decision to freeze contacts, with a foreign ministry source quoted by the official news agency IRNA as saying ties were already "cold and inactive."
British military chiefs used maps and GPS coordinates to affirm that the navy personnel were 1.7 nautical miles within Iraqi waters at the northern end of the Gulf.
The Iranian embassy in London insisted that the British personnel had "illegally entered" up to 500 metres within Iranian territorial waters.
British Prime Minister Tony Blair emphasised his country's determination in the dispute.
"It is now time to ratchet up the diplomatic and international pressure," Blair told lawmakers, adding that "there was no justification whatever" for the detention of the sailors.
There has been speculation that Tehran could use the British personnel either to trade for five Iranians being held by US forces in Iraq or to seek concessions over Iran's nuclear drive.
Speaking for the European Union, German Chancellor Angela Merkel called Iran's action "unacceptable" and renewed a call for the soldiers' release.
NATO Secretary General Jaap de Hoop Scheffer also called for their immediate release.
The United States, which has already voiced "concern and outrage" over the incident, denied that an unusual exercise involving two US aircraft carrier strike groups in the Gulf was aimed at raising tensions with Iran.
Oil prices were at six-month highs over the growing tensions at around 64 dollars a barrel in Asian trade.