Spain's conservative People's Party is set to win the most seats in the lower house of parliament in next month's national election, far ahead of the ruling Socialist Workers' Party (PSOE), a poll released by El Pais newspaper showed on Monday.

The survey, carried out between June 12 and 14, showed the PP widening its lead over Prime Minister Pedro Sanchez' PSOE, pollster 40DB said.

The poll, commissioned by El Pais newspaper, estimated that the PP would get between 128 and 142 seats in the 350-member lower house, up from 131 in the previous poll held between May 31 and June 1. The PSOE would get between 99 and 109 seats, it showed, compared with 107 in the previous such survey.

An alliance between the PP and the far-right Vox party, seen garnering between 37 and 41 seats, would exceed the 176 seat absolute majority in the lower house needed to rule.

Sanchez on May 29 called a surprise snap election after his party and its junior coalition partner Podemos were routed in regional and municipal ballots. Sanchez said he would lead his party and seek to remain prime minister.

The July 23 election is shaping into a binary choice between those opposed to a government that would include the far-right Vox and those who oppose the current minority coalition that includes the far-left Podemos.

After the regional and municipal elections, Podemos allied with other far-left groups into a new party called Sumar, which would get between 34 and 36 seats in the July elections, 40DB said. The previous poll carried out between May 31 and June 1 had attributed 41 seats to Sumar.

The remaining seats would go to small regionalist parties. (Reporting by Inti Landauro Editing by Gareth Jones)