Details of the case first emerged in September 2020 when prosecutors unveiled an investigation which centred on the recruitment of a driver to spy on the PP's former treasurer, Luis Barcenas.

At the time of the alleged spying, Barcenas was at the heart of a judicial probe over a kickbacks scheme which financed the party known as the Gurtel case, for which he was later jailed for 33 years.

The aim of the alleged spying was to find out what dirt he had on party officials.

Quizzed for 90 minutes as a defendant at Spain's National Court, Maria Dolores de Cospedal, the party's former secretary general, denied having any hand in recruiting the driver, judicial sources said.

Although she admitted meeting "several times" with notorious former police chief Jose Manuel Villarejo, she said she had never asked him to work for her.

Last year, prosecutors said they were looking into widespread evidence that Cospedal and former interior minister Jorge Fernandez Diaz, both of whom served under former PP prime minister Mariano Rajoy, were involved in the spying scandal.

Public prosecutors allege the driver received 2,000 euros ($2,370) per month, as well as the promise of a job in the police force, in exchange for obtaining information regarding where Barcenas and his wife hid "compromising documents" about the PP and its senior leaders, papers from the investigation show.

The probe into the spying affair, known as "Operation Kitchen", is one of several which have been opened based on searches carried out following the arrest of Villarejo, a former police commissioner who for years secretly recorded conversations with top political and economic figures to be able to smear them.