The case centres on allegations that a driver was paid out of state coffers to spy on the former treasurer of the main opposition Popular Party (PP), Luis Barcenas.

The high-profile affair has been dubbed “Operation Kitchen” because the code name of the alleged informant was “the cook”.

Fernando Diaz, 72, who served as interior minister between 2011 and 2016, is accused of embezzlement, crimes against privacy and concealment for his alleged role in the affair.

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 ruling led to the ouster of the then prime minister Mariano Rajoy in a confidence vote in parliament several days later.

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

The probe into the spying affair is one of several which have been opened based on searches carried out following the arrest of in 2017 of Jose Manuel Villarejo, a former police commissioner who for years secretly recorded conversations with top political and economic figures to be able to smear them.

Diaz has said he knew nothing about the alleged spying but public prosecutors have called for him to be sentenced to 15 years in jail, according to a copy of the charge sheet published Friday.

Prosecutors are seeking a jail term of 19 years for Villarejo. A date for the trial has not yet been set.