Six months ahead of a parliamentary election, a new opinion poll published Thursday shows Poland's governing liberals are losing ground to their conservative and social democratic opposition rivals.

The Civic Platform (PO) of Prime Minister Donald Tusk scored 39 percent support, a drop of five percent from last month, according to a survey by the TSN OBOP polling group.

The Law and Justice (PiS) conservative opposition tallied 27 percent support, up three percent over last month.

Markedly sceptical towards Poland's neighbours Russia and Germany as well as towards the European Union, the PiS is led by Jaroslaw Kaczynski, the surviving twin of Lech Kaczynski who was killed a year ago along with 95 other mostly senior Polish figures in an air crash in Russia.

The ex-communist social democrats (SLD) gained three percent support since March, raising their tally to 18 percent.

The PSL farmers' party, the junior governing coalition partner, held on to its previous six percent support, allowing it to surpass the five percent voter support threshold allowing parties to enter parliament.

Although no date has been set for the election, it must be held this autumn, most likely in October.

If the PO were to be re-elected, it would be a first since the 1989 advent of democracy in Poland which has seen power shifts from party to party in all seven previous parliamentary elections.

The election will be held as Poland holds the six-month rotating presidency of the European Union, which it assumes July 1.