Clara Ponsatí, the Catalan academic facing extradition to Spain, has accused the Spanish judiciary of pursuing an illegal vendetta against Catalan nationalists.

Ponsatí told a fringe meeting at the Scottish National party’s spring conference that last October’s referendum on Catalan independence was entirely legal, even if it had not been supported by the government in Madrid.

“It was the duty of the Catalan authorities, who had a mandate for the referendum, to organise a referendum. We were obliged to do it. Besides it was not illegal. We have done nothing illegal,” she said.

“The Spanish authorities have manipulated the judiciary, have manipulated the reading of the law, have manipulated the facts and they’ve opened these charges which are totally, totally illegal themselves. What is illegal is what the judiciary is doing in Spain now. That is illegal.”

Ponsatí, an economics professor at St Andrews University in Scotland, faces a four-week extradition hearing later this summer after the Spanish authorities issued a European arrest warrant.

The Spanish courts accuse her of violent rebellion and of misuse of public funds in organising the referendum. The staging of the vote divided Catalonia, and Madrid insists it was illegal and unconstitutional because it was not authorised as required by Spain’s parliament.

Ponsatí’s lawyer, Aamer Anwar, says there is “not a scrap of evidence” to support the charges against her, which carry maximum sentences of 25 years and eight years in prison respectively. Other Catalan leaders, including the then president Carlos Puidgemont, face a similar extradition case in Germany.

Anwar told the meeting that violent attacks by Spanish civil guards on voters at some polling stations on 1 October carried “shades of Franco”, and were reminiscent of the suppression of human rights during the regime of the fascist dictator who ruled from 1939 to 1975.

SNP activists and some Scottish MPs have rallied to Ponsatí’s cause. Her legal defence fund has reached £270,000, but Anwar has told her supporters she needs £500,000 to cover all her expected legal costs given the complexity of the case.

Joanna Cherry, an SNP MP and QC, told the meeting that nine political and civic leaders who backed the referendum in October remained in prison, with 19 people due on trial in Madrid in August.

She and Anwar said the Ponsatí and Puidgemont extradition cases had increased concerns that some EU member states were abusing the European arrest warrant system to pursue political opponents rather than criminals. The cases also raised concerns about judicial independence, they said.

St Andrews University has officially backed Ponsatí, suggesting the extradition attempt against her is politically motivated. The Courier newspaper, based in Dundee, has reported that 10 or more academics at St Andrews including Spanish staff are unhappy it has done so and asked for its statement to be retracted.

Much rests on whether the newly appointed Socialist-led government in Madrid, which came to power in part as a result of a deal with Catalan parties, starts talks with the Catalan authorities in Barcelona and agrees a political solution to the crisis.