Protesters have insulted and jeered at the former treasurer of Spain's ruling Popular Party as he left prosecutors' offices where he was questioned about documents which allegedly show he once paid slush fund money to leading party members, including Prime Minister Mariano Rajoy.

People shouted "thief" and "give the money back" at Luis Barcenas as he left the anti-corruption prosecutors' office Wednesday.

Barcenas was being questioned after Spanish newspaper El Pais last week published what it called Barcenas' "secret papers," with copies of alleged records from several years ago showing names and amounts received. The money was allegedly mostly paid by construction companies.

Both Barcenas and the Popular Party claim the documents are false and deny any wrongdoing.

Barcenas declined to talk to reporters Wednesday.