Greek opposition MPs are seeking further clarification over allegations 28 Pakistani migrants were abducted and mistreated by intelligence agents.
Left wing politicians claim there has been a cover-up and that national sovereignty is at stake.
Earlier a Greek newspaper published names of Greek and UK agents allegedly involved in the operation, which has been denied by both governments.
The Pakistanis say they were seized in Greece after the 7 July London bombs.
They say they were interrogated over a period of several days and mistreated.
UK gag order
Greek weekly paper Proto Thema at the weekend published what it said was the name of a British spy chief and 15 Greek agents involved in the abduction and mistreatment of the migrants.
It said the Briton named was a diplomat who was the Athens chief of Britain's intelligence service MI6.
The UK government has forbidden the British media from naming the man.
The Greek intelligence agency earlier said it deplored the naming of the officers.
The British government has described allegations of ill-treatment of migrants following the London bombings as "utter nonsense" and "farfetched".
The Greek intelligence agency, EYP, condemned the paper for what it called "illegally endangering the safety of its agents in the field".
Greek opposition MPs called on Tuesday for an expanded judicial investigation, AP news agency reported.
"It is clear there has been a cover-up of this issue at a high level," said Nikos Voutsis of the Left Coalition party.
According to the Socialist party, a hearing on the abduction claims has been set for 11 January.
On Sunday the men's lawyer filed a petition with the Greek parliament to force the government to answer more questions.
The BBC's Malcolm Brabant in Athens said that in the past few weeks more details had emerged of the alleged mistreatment by Greek-speaking agents.
One detainee has alleged that he had a gun placed in his mouth; one said he was beaten; and another claimed he saw a third detainee being beaten up, our correspondent says.
All 28 said they had hoods placed over their heads and some were held incommunicado for seven days.