Labor says legal advice from Poland shows it has an “open and shut” case that Liberal MP Jason Falinski is a dual national, threatening to ensnare the first week of Parliament in a fresh round of trench warfare on citizenship.

Mr Falinski swiftly dismissed the advice as “just wrong”. The MP, who holds the safe Sydney seat of Mackellar, previously held by Bronwyn Bishop, by 16 per cent has long been eyed by Labor as the government MP under the longest citizenship shadow.

A Polish expert consulted by Labor has said information from the Office of Citizenship in Warsaw shows “Mr Falinski’s father is indeed a Polish citizen as he migrated from Poland on a Polish passport”.

Jolanta Wolski, an immigration consultant who divides her time between Poland and Australia, said this made Mr Falinski Polish by descent.

Legal advice from the Krakow-based firm Lexmotion, also obtained by Labor, states that “Polish passports are conclusive proof of Polish citizenship, as they are (and were) issued to Polish citizen[s] only.”