Dutch Prime Minister Jan Peter Balkenende appears to have suffered considerable damage over his government's handling of a row in the royal family
The couple have filed a complaint against the state
Newspaper reports on Thursday suggested that Mr Balkenende had given a faltering performance in parliament the previous day as he attempted to explain an investigation into the fiance of Queen Beatrix' niece.
The government was asked why ministers were unaware that the investigation had been ordered by the queen's office.
Princess Margarita and her husband, commoner Edwyn de Roy van Zudewijn, on Tuesday filed a law suit accusing the state of indiscretion.
Prime Minister Balkenende suffered serious political damage in the debate - his defence of his letter and of the activities of the queen's office failed to convince parliament
The princess says she found bugging devices in her home, and has accused her aunt of abusing her authority to obtain Mr van Zudewijn's tax and social security files.
'Failure to convince'
As the princess and her husband watched from the public gallery, Mr Balkenende told MPs that the investigation was acceptable as a security measure for anyone marrying into the royal family.
The prime minister said mistakes had been made and promised that in future the queen could only request such an inquiry with his authorisation.
Balkenende: Admitted mistakes
But the newspaper De Volkskrant said he had not come across well: "Prime Minister Balkenende on Wednesday suffered serious political damage in the debate...
"Balkenende's defence of his letter and of the activities of the queen's office failed to convince parliament."
In the Netherlands, the prime minister bears the ultimate political responsibility for the sovereign's actions.
The princess and her husband are also suing former Prime Minister Wim Kok for alleged fraud, forgery and divulging state secrets.
Mr van Zudewijn has also demanded an apology from the queen.
The queen's office is said to have authorised the investigation
The BBC's Geraldine Coughlan in The Hague says a string of new measures with regard to security checks on individuals is sure to follow the scandal, but the upheaval will not leave the royal family unscathed.
A recent poll showed 54% of Dutch people believe the row has damaged the well-respected monarchy.
The feud is unprecedented in the Netherlands, where the queen has in the past declared that she wanted "no English situations" - a reference to the scandals that have beset one of the more prominent European royal families.