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."
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.
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.
