Mariano Rajoy, the Spanish prime minister, was on Wednesday implicated in an alleged smear campaign after taped conversations appeared to show his interior minister asking a top anti-corruption official for help in discrediting political rivals.

Just four days before Spaniards vote in the country's second general election in six months, tapes have emerged in which the minister, Jorge Fernández Díaz, can be heard discussing potential allegations of corruption against Catalan officials from the region’s pro-independence government.

In one of the recorded excerpts, after discussing a series of possible allegations and how they might be leaked to the press, Mr Fernández Díaz says: “The prime minister knows about it […] He’s a very discreet man, and of course his right hand does not know what his left hand is doing”.

The conversations between the interior minister and the head of Catalonia's Anti-Fraud Office, published by digital newspaper Público, took place in 2014 in the run up to a wildcat 'referendum' called by the leaders of the semi-autonomous region, which Madrid resolutely opposed.

During the conversation, Daniel de Alfonso, the anti-fraud official, allegedly lays out several leads for possible offences committed by various pro-independence politicians or their relatives, but adds they are "weak".