The collateral deal was a condition of Finland's participation in the EU's bailout programme for Greece.

Keeping the public in the dark has drawn much criticism. Olli Mäenpää, a professor of administrative law at the University of Helsinki, says everything but potential business secrets should have been disclosed.

“The other signing party has demanded it be kept secret,” says Hetemäki, who signed the agreement on behalf of Finland. He says Greek banks would not have agreed to the deal without the promise of confidentiality.

Hetemäki rebuffs allegations that Finland bowed to Greek demands and says secrecy on the details has not obstructed public debate on the issue.

Last month MPs were given the opportunity to inspect documents related to the deal in Parliament but were forbidden to discuss the details in public.

The deal only Finland wanted

The collateral deal aims to protect Finnish taxpayers from the costs of funding the second bailout for Greece. Observers, however, say Finland did not secure favourable terms in the deal, suggesting that election promises weighed more in the government's guarantee demands than any other considerations.

Finnish anger over eurozone bailouts was seen as a major factor in the surge in popularity of the Finns Party in last spring’s parliamentary elections.