The PSOE led by Pedro Sanchez would secure some 32 percent of the vote and between 133 and 150 seats in the 350-seat Congress up from the 123 seats it won in April.

But there is a flaw in the findings: the survey published by the CIS Research Institute on Tuesday was conducted between September 21 and October 13, before the controversial sentencing of 12 Catalan separatist leaders sparked widespread protest in Catalonia.

It also judged opinion before the high-profile exhumation of General Francisco Franco, an event that is also considered to have bearings on how people will vote next month in the fourth election in as many years.

But the data does show that it would be possible for Sanchez to form a government if he can secure the support of either the radical left Unidas Podemos or the centre-right Ciudadanos.

Support from either party would take Sanchez above the magic 176 seats needed for a majority in Spain’s lower chamber and exclude the need for support from the Catalan separatist parties.  

The CIS poll predicted that the Popular Party led by Pablo Casado would see its support rise from 16.7 percent to 18.1 percent and support for Ciudadanos fall from 15.9 percent to 10.6 percent.

Far-right newcomers Vox would also see its support fall from 10.3 percent to 7.9 percent and a corresponding drop in the number of seats from the 24 it secured in April to between 14 and 21.

Support for Podemos would increase slightly from 14.3 to 14.6 percent.

The survey involved 17,650 interviews, carried out in 1,091 municipalities in 50 provinces, as well as Spain’s North African cities Ceuta and Melilla with a margin of error of plus or minus 0.75 percent.