Mariano Rajoy, who was premier from 2011-2018, and Jose Maria Aznar, who served from 1996-2004, are scheduled to testify on March 24 in a trial focused on an alleged system of parallel bookkeeping used by the PP to manage undeclared funds.

The accounts were run by Luis Barcenas, who served as the PP treasurer between 1990 and 2009 during which time first Aznar and then Rajoy led the party.

The high-profile trial opened on February 8 at the National Court in Madrid and will run until May.

For nearly 20 years, the alleged slush fund was fed by donations from businessmen and used to pay bonuses to PP leaders and collaborators.

It also funded the renovation of the party’s Madrid headquarters, Barcenas has said.

Rajoy has always denied any knowledge of the system, although Barcenas has testified he was “perfectly aware” of it, telling the court last week that he was one of those who received envelopes of cash in the period before he became premier.

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“I gave them an envelope containing the amount they were owed,” he said, identifying the recipients as eight senior PP figures, among them Rajoy.

Details of the accounts emerged in the so-called “Barcenas papers” which were first published by El Pais newspaper in 2013.

Barcenas himself is currently serving a 29-year sentence over the so-called Gurtel case which centred on a vast system of bribes given to former PP officials in exchange for juicy public contracts between 1999 and 2005.