Home Secretary Theresa May will come under pressure to reveal exactly what Europe's human rights court told her officials about the deadline to deport Jordanian terror suspect Abu Qatada.
David Cameron backed May on Monday over the row which risks seeing the radical cleric, described by a judge as Osama bin Laden's right hand man in Europe, freed and back on Britain's streets within weeks.
MPs will question the Home Secretary on Tuesday over the confusion, which centres on whether the three-month appeal deadline from the court's original decision on January 17 expired on the night of April 16 or 17.
The Prime Minister has insisted the Home Office "checked repeatedly" with the European Court of Human Rights (ECHR) about when the deadline expired and has denied the Government made a "complete mess" of getting Qatada out of the country.
The Home Office was "very clear" about the date, had checked with the court and considered the precedents, Cameron said.
But he did not say what the court told the Home Office when it asked about the deadline.
May has also insisted that the appeal by the radical cleric's lawyers should be thrown out because it missed the deadline, but advice from the research department of the Council of Europe - which is responsible for the court - suggests otherwise.
Qatada, 51, was arrested by officers from the UK Border Agency (UKBA) on the morning of Tuesday April 17, just hours after the Home Office said the time for any appeal was up.
But Qatada's lawyers claim their appeal to the Strasbourg-based court, made at 11pm local time (10pm BST) on April 17, was just before the midnight deadline.
And the row could lead to Qatada being back on British streets in days after the senior British immigration judge in the case, Mr Justice Mitting, said last week he would reconsider releasing Qatada on bail "if it is obvious after two or three weeks have elapsed that deportation is not imminent".
A panel of judges at the human rights court will now decide whether the appeal was in time or not. If the deadline had expired, the judges have no discretion to allow the appeal to be considered by the court's Grand Chamber.
Shadow home secretary Yvette Cooper called on May "to come clean, to provide the advice she was given and who knew what and when" when she appears before MPs on the Commons Home Affairs Select Committee.
The Home Secretary is also expected to be questioned about concerns that London's Heathrow airport may not be able to cope with the arrival of thousands of extra passengers for this summer's Olympic Games.
Planes could be left on runways and there could be long queues at immigration, the Commons Culture, Media and Sport Committee warned in a letter to Culture Secretary Jeremy Hunt.
Tourists could be deterred from returning to Britain and there seemed to be no contingency being made for the extra time needed to unload passengers this summer, they said.
Government plans for increased monitoring of emails and internet use, which have been strongly criticised by civil liberties campaigners, will also be scrutinised.
The proposals would allow Government listening post GCHQ to monitor internet traffic - times, dates, numbers and addresses - in real time.
Keith Vaz, the committee's chairman, said: "With the Olympics less than 100 days away, airport border controls under intense pressure, police absorbing a far-reaching review of their pay and conditions, and the deportation of Abu Qatada, the Home Secretary's appearance before the committee could not be more timely.
"We will also take the opportunity to begin scrutinising Government surveillance plans, in particular the interception of communications data and the implications for personal privacy."