Officials say GPS data shows the personnel were in Iraqi waters
MoD news briefing
Vice Admiral Charles Style said the sailors had been "ambushed" in the Gulf after searching a vessel and their detention was "unjustified and wrong".
Tony Blair said it was time to "ratchet up" pressure on Iran, with whom the UK has now suspended bilateral contacts.
Reports suggest the only woman among the group will be freed shortly.
An Iranian foreign ministry spokesman is quoted as saying Faye Turney, 26, would be released either later on Wednesday or on Thursday.
Iran has insisted the group were in its waters when they were taken last Friday.
The eight sailors and seven marines, based on HMS Cornwall, which has its home port in Plymouth, were taken at gunpoint by Iranian Revolutionary Guards after they had searched a merchant vessel.
UK VERSION OF EVENTS 1 Crew boards merchant ship 1.7NM inside Iraqi waters
2 HMS Cornwall was south-east of this, and inside Iraqi waters
3 Iran tells UK that merchant ship was at a different point, still within Iraqi waters
4 After UK points this out, Iran provides alternative position, now within Iranian waters
UK version in more detail
Iranian foreign minister Manouchehr Mottaki told Turkey's CNN-Turk television the 15 - thought to be at the guards' base in Tehran - were in "completely good health".
Iran's embassy in London also issued a statement in response to the UK data, in which it said the sailors and marines had been 0.5 km inside Iranian waters at the time they were seized.
The statement, quoted by the official IRNA news agency, said "the governments of Iran and Britain have the ability to solve the incident through contacts and close co-operation".
At a briefing in London, the Ministry of Defence said it "unambiguously contested" Iran's claims that the Royal Navy personnel had strayed into Iranian waters.
Speaking later, Mr Blair told MPs it was time to increase pressure on Iran "in order to make sure the Iranian government understands their total isolation on this issue".
The seizure of the personnel was "unacceptable, wrong and illegal" and the UK was now in talks with all its key allies and partners, he said.
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Mr Blair added: "Our thoughts are with the servicemen and the servicewoman and their families, and their safe return is our paramount concern."
The prime minister said: "These personnel were patrolling in Iraqi waters under a United Nations mandate. Their boarding and checking of the Indian merchant vessel was routine - there was no justification therefore for their detention."
Mr Blair said the personnel had been "doing their job" and the government would be talking to international partners in Nato and the UN to reach a "sensible" solution.
The UK government said the Iranians initially said the merchant vessel searched by the navy personnel had been at a point within Iraqi waters, before later providing a second, alternative position, within Iranian waters.
In a statement to the Commons, Mrs Beckett said: "We find it impossible to believe, given the seriousness of the incident, that the Iranians could have made such a mistake with the original coordinates."
She told MPs that Britain were suspending bilateral contacts with Iran until the navy personnel were released.
HAVE YOUR SAY The country of Iran needs to have a good long hard look at how this situation will look to the rest of the world
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Send us your comments Iranian view on stand-off
Shadow foreign secretary William Hague said: "The seizure of our personnel was clearly unjustified and the evidence the foreign secretary and the MoD has presented shatters the credibility of any claim they were operating in Iranian waters."
BBC security correspondent Frank Gardner said the freeze on ties between the two countries meant that until the Britons were returned there would be "no inward or outward visits to Iran" and no UK visas would be granted to Iranian officials.
''The Australian'' has reported that an internet website "run by associates of Mahmoud Ahmadinejad" states that the 15 British sailors who were arrested by Iranian Revolutionary Guards could face charges of espionage. The source website for this claim remains unknown; however, ''Rajanews.com'', a news website run by some of supporters of Ahmadinejad said on their website: "If the charges of espionage is brought against them the result would be heavy punishment by current law."

"If it is proven that they deliberately entered Iranian territory, they will be charged with espionage. If that is proven, they can expect a very serious penalty since according to Iranian law, espionage is one of the most serious offenses," said the news report which also called the sailors "insurgents." Individuals who are tried and found guilty of espionage or spying would be penalized by death, according to Iranian law.
An inflatable British patrol boat similar to the two seized by Iran on March 23, 2007. (File photo: Patrol boat assigned to HMS ''Cardiff'' seen in Iraq in 2002)
The Iranian government initially gave the position of the incident as being ''outside'' Iranian territorial waters. General Alireza Afshar, Iran's top military general, then stated that the sailors were engaged "in illegal and suspicious activities" inside Iranian waterways at the time of their detention and that the sailors "have admitted to violating the territorial waters of the Islamic republic". After the UK queried the statement by General Alireza Afshar, the Iranian government gave a revised position for the incident, now placing it ''inside'' Iranian territorial waters.

Reports also say that the sailors are being held until five Iranian guards, detained in Iraq by the United States early in 2007, are released to the Iranian government.



"As soon as the corps’s five members are released, the Britons can go home," an unnamed source close to the command of Qods Force, who also said that Iran's supreme leader, Ayatollah Khamenei approved of the trade off.

The sailors and marines, from the frigate , had been inspecting, in accordance with UN Security Council Resolution 1723, a ship that was believed to be smuggling cars into Iraq, though it was subsequently cleared after inspection when Iranian gunboats surrounded the sailors and arrested them at gunpoint.

Reports also say that the sailors were taken to the Iranian capital of Tehran where they are allegedly going to appear before a court. It is not known when they will appear before the court in Iran or when the hearing will be held.

As a result of the detention of the sailors, the United Kingdom has activated their "", which is Britain's crisis management team as the U.K. denies that the sailors were in Iranian waters. Tony Blair, the U.K.'s Prime Minister, calls the situation "unjustified and wrong."

"This is a very serious situation and there is no doubt at all that these people were taken from a boat in Iraqi waters. I hope the Iranian government understands how fundamental an issue this is for us. They should not be under any doubt at all about how seriously we regard this act, which was unjustified and wrong. It is simply not true that they went into Iranian territorial waters," Blair claimed during a news conference today who also stated that the situation could be resolved within the next couple of days.

"The quicker it is resolved, the easier it will be for all of us," added Blair.

In a press release March 25,  Minister  stated, "We've been insisting that the sailors should be released immediately - there is no reason to hold them - that they should be released unharmed and that we should be in a position to assure their families that they are in good health and that they're safe."

Triesman indicated that meetings have taken place with Iranian officials over the release of the seized British sailors, and that "they're delicate discussions."