The chairman of the Commons home affairs committee has demanded an explanation from police over why the partner of the Guardian journalist who wrote a series of stories revealing mass surveillance programmes by the US National Security Agency (NSA) was detained for nine hours under the Terrorism Act at London's Heathrow airport.
On Sunday, David Miranda, the partner of Glenn Greenwald, the first to interview American whistleblower Edward Snowden, was stopped at 8.30am on his way home to Rio de Janeiro following a trip to Berlin.
Labour MP Keith Vaz said the events were an "extraordinary twist" to an already complex story. Speaking on BBC Radio 4's Today programme, he said: "Of course it is right that the police and security services should question people if they have concerns or the basis of any concerns about what they are doing in the United Kingdom.
"What needs to happen pretty rapidly is we need to establish the full facts - now you have a complaint from Mr Greenwald and the Brazilian government, they indeed have said they are concerned at the use of terrorism legislation for something that does not appear to relate to terrorism, so it needs to be clarified, and clarified quickly.
"What is extraordinary is they knew he was the partner [of Greenwald] and therefore it is clear not only people who are directly involved are being sought but also the partners of those involved.
"Bearing in mind it is a new use of terrorism legislation to detain someone in these circumstances ... I'm certainly interested in knowing so I will write to the police to ask for the justification of the use of terrorism legislation - they may have a perfectly reasonable explanation."
Vaz added: "But if we are going to use the act in this way then at least we need to know so everyone is prepared."
The detention was also condemned by civil liberties groups. Shami Chakrabarti, the director of Liberty, said: "David Miranda's chilling 9-hour detention was possible due to the breathtakingly broad Schedule 7 power, which requires no suspicion and is routinely abused.
"People are held for long periods, subject to strip searches, saliva swabbing and confiscation of property - all without access to a publicly funded lawyer. Liberty is already challenging this law in the Court of Human Rights but MPs disturbed by this latest scandal should repeal it without delay."
Greenwald and Miranda reunited at Rio de Janeiro's International Airport
According to The Guardian Miranda was questioned under schedule 7 of the Terrorism Act 2000 which applies only at airports, ports and border areas, allowing officers to stop, search, question and detain individuals.
The 28-year-old was held for nine hours - the maximum the law allows before officers must release or formally arrest the individual - before being released without charge.
But the newspaper reported his electronic possessions including his mobile phone, laptop, camera, memory sticks, DVDs and games consoles were confiscated.
A Downing Street spokesman said: "The government takes all necessary steps to protect the public from individuals who pose a threat to national security.
"Schedule 7 forms an essential part of the UK's border security arrangements. But it is for the police to decide when it is necessary and proportionate to use these powers."
Greenwald said the detention of his partner was "a profound attack on press freedoms and the news gathering process".
"To detain my partner for a full nine hours while denying him a lawyer, and then seize large amounts of his possessions, is clearly intended to send a message of intimidation to those of us who have been reporting on the NSA and GCHQ.
"The actions of the UK pose a serious threat to journalists everywhere. But the last thing it will do is intimidate or deter us in any way from doing our job as journalists. Quite the contrary: it will only embolden us more to continue to report aggressively."
Labour MP Tom Watson called for parliament to look into what he said could be seen as an attempt to "get the genie back into the bottle" when it returns in September.
He also questioned whether Home Office ministers were informed of the move, which he described as "clearly an embarrassment to the Government".
"What I think we are going to see is this is sort of the intelligence services overstepping the mark - they are clearly trying to intimidate Glenn Greenwald - and that's an attack on journalism," Watson told the BBC. "I think politics needs to intervene to make sure it doesn't happen again."