"The secessionist process was the worst episode of disloyalty in the history of our democracy," Deputy Prime Minister Soraya Saenz de Santamaria told a Senate committee.
"But the worst betrayal was to Catalans who genuinely believed in independence. They were the ones who were led to believe that (their dream) was about to come true, whereas in fact it was all a big show, a 'symbolic' episode," she said.
"A fake, in the full sense of the word," she said, adding that the campaign had been "founded on post-truth".
Saenz de Santamaria also said separatist leaders had privately admitted that it was "impossible" for Catalonia to function as an independent state.
The deputy prime minister's statement came as she presented her findings to a Senate committee, after she was tasked to run the region following a unilateral independence declaration by Catalonia's axed parliament on October 27th.
Spain is poised to back Catalonia's regional autonomy once a new government takes the reins following a pivotal election on Thursday.
As the decisive moment nears, secessionist and pro-unity candidates are neck-and-neck in the polls.
Saenz de Santamaria meanwhile accused the deposed Catalan government of diverting regional funds to finance their objectives, including more than €10 million ($11.8 million) to pay their representatives abroad.
"Meanwhile, entire hospital services were shut," she said.
She also accused the deposed government of abandoning its responsibilities towards the education, health and judicial sectors, focusing instead on its independence drive.
Spain was plunged into its worst political crisis since democracy was reinstated following dictator Francisco Franco's death in 1975, after the Catalan government pushed ahead with a banned independence referendum on October 1st.
Catalonia's regional election on Thursday, a critical moment for both sides of the divide, will chart the course of the secession crisis.