Costa told Portuguese television channel SIC in an exclusive interview on Tuesday night that it was also "highly probable" that the country's president, Marcelo Rebelo de Sousa, would be reelected if he were to stand again for president in 2021.

Speaking to journalists following the interview, before leaving SIC's premises, Costa played down the issue of whether the PS was seeking an absolute majority in the next elections, saying that he would govern under current conditions.

Costa also said that absolute majorities are not favoured under Portugal's electoral system of party-list proportional representation.

The PS has since 2015 governed with a minority of seats in parliament, with the support of smaller leftist parties with which it has forma agreements.