Vaz, the chairman of the influential parliamentary Home Affairs Select Committee, will write to the police seeking full facts of the nine-hour questioning of David Miranda, who is the partner of journalist Glenn Greenwald -- behind US whistleblower Edward Snowden's worldwide spying revelations.
"It is an extraordinary twist to a very complicated story," Vaz told BBC today. "I will write to the police to ask for the justification of the use of terrorism legislation -- they may have a perfectly reasonable explanation."
Greenwald has written a series of stories revealing mass surveillance programmes by the US National Security Agency.
His live-in partner, Miranda, was held as he passed through London's Heathrow airport on his way from Berlin to Rio de Janeiro.
The Brazilian national reportedly had his mobile phone, laptop, DVDs and other items seized before he was released.
"This measure is without justification since it involves an individual against whom there are no charges that can legitimate the use of that legislation. The Brazilian government expects that incidents such as the one that happened to the Brazilian citizen today are not repeated," a Brazilian government statement said.
Under the Terrorism Act 2000, British police can hold someone at an airport for up to nine hours -- but the power must be used appropriately and proportionately and is subject to independent scrutiny.
According to the Home Office, more than 97 per cent of examinations last less than an hour.
"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 UK. 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," Vaz, a Labour MP from Leicester, stressed.
The Home Office refused to comment on the detention of Miranda, stating that it was a matter for the police.
In a brief statement, a Scotland Yard spokesperson said: "At 08:05 on Sunday, August 18, a 28-year-old man was detained at Heathrow airport under Schedule 7 of the Terrorism Act 2000. He was not arrested. He was subsequently released at 17:00."
Since June 5, Greenwald has been writing about the NSA's electronic surveillance programmes, detailed in thousands of files passed to him by Snowden.
'The Guardian' has also published a number of stories about blanket electronic surveillance by Britain's GCHQ, also based on the documents.
While in Berlin, Miranda visited Laura Poitras, the US filmmaker who has also been working on the Snowden files with Greenwald and the newspaper, which had paid for Miranda's flights.
"This is a profound attack on press freedoms and the news gathering process... 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," Greenwald said.
British MPs ask Singh whether India in loop on visa bonds
'Don't boycott Sochi Olympics, wave gay flags instead'
US snooping programme had one server in India: Report
US lawmaker compares Snowden with Mahatma Gandhi
Obama calls Merkel, discusses NSA snooping