Jan Cienski in Warsaw -

Polish prosecutors have brought the "Waitergate" scandal bubbling back to the surface as they announced a probe - an ominous turn for the ruling Civic Platform (PO) party. 

Warsaw prosecutors said this week they will take a closer look at the secret recordings. In particular, they will decide whether Interior Minister Bartlomiej Sienkiewicz, National Bank of Poland Governor Marek Belka and Prime Minister Donald Tusk violated any laws during a dinner conversation thought to have been taped illegally by staff at a restaurant.

The details of the discussion, which reportedly took place in summer 2013, were splashed across the pages of the Wprost news weekly in June. That sent PO into frenzied damage limitation, and it faced down more than one no-confidence vote in parliament.

According to the transcript, Belka and Sienkiewicz discussed possible risks to the Polish economy, and PO's chances of winning re-election in next year's parliamentary vote. As a price for NBP support in propping up the economy, Belka asked for the removal of then-finance minister Jacek Rostowski. 

Jacek Rostowski lost his job in November, while changes in the bank's statue are working their way through parliament. Both men have denied any wrongdoing in the press. 

However, prosecutors have been asked to intervene by a group of opposition politicians. Przemyslaw Nowak, spokesman for the Warsaw regional prosecutor's office, says the infraction being investigated is "undermining the independence of the NBP through an informal agreement struck in July 2013 by the prime minister and the president of the NBP via the interior minister."

Although the government appears sanguine about the probe, the move is a blow to Tusk. Waitergate had been pushed out of the news in recent weeks by the increasingly dire events in neighbouring Ukraine. The opening of the investigation returns the affair to the front pages.

The scandal has already seen PO battered in opinion polls. One recent survey, by the Homo Homini organization, sees the main opposition Law and Justice (PiS) taking 36% support, while Civic Platform lags on 25%. That shows PiS starting to break through the one-third of voter support that has been the populist party's ceiling for several years. Many centrist voters remain wary following it's controversial government in 2005-2007.

The probe will also distract PO as it tries to regain its balance ahead of local government elections set for November. Lukasz Lipinski at Polityka Insight writes: "The prosecutor's decision could deepen the negative consequences of the affair for PO, the prime minister and the government in opinion polls."