Ponsati, a former Catalan education minister who is now a professor at Scotland's University of St Andrews, is one of the Catalan leaders being sought by the Spanish courts for organizing a referendum on independence in October previous year that was deemed illegal under Spanish law.
A Spanish judge last week issued worldwide and European arrest warrants for Ponsati and other separatist leaders, including former regional president Carles Puigdemont.
She attended St Leonards police station in the capital in response to an arrest warrant charging her with "violent rebellion and misappropriation of public funds" over her role in Catalonia's independence referendum a year ago.
"Scotland has been a true friend to Catalonia in her darkest hours", said Anwar.
Inigo Mendez de Vigo, a Spanish government spokesman, denied the separatists were "victims", insisting their "criminal actions" were an "attack" not only against Spain but the European Union.
"The Spanish authorities wish to extradite Clara on charges of violent rebellion and misappropriation of public funds for helping to organise the referendum".
"Clara views these charges as "political persecution" and submits that her human rights and justice can not be guaranteed in the Spanish Courts".
A crowd-funding appeal set up on Wednesday to pay for her legal costs had raised more than £158,000 by mid-afternoon.
Other senior figures from the former Catalan government have been apprehended across Europe on the foot of EAWs issued by Spain, including former president Carles Puigdemont in Germany.
"Clara remains defiant and resolute and believes that the Spanish Government will never be able to crush the spirit of the Catalan people".
It is expected police will place her under arrest and formally serve the European Arrest Warrant on her.
"She does not believe that the Spanish courts can guarantee independence, human rights or justice".
Anwar went on to reiterate his consistent argument, expressed in his interview with CommonSpace yesterday, that "it is absolutely right that the independence of the judiciary in Scotland in respected and that no Government should interfere in that process".
Ponsati was a minister in the Catalan government when it declared independence from the rest of Spain following a referendum in October.
The academic is then due to appear from custody at an initial extradition hearing at Edinburgh Sheriff Court later on Wednesday.
Anwar placed particular emphasis on Ponsati's desire to that "the many hundreds of thousands of ordinary people, especially in Scotland, who have shown her such love and support".
The professor at the University of St. Andrews returned to Scotland in March after fleeing Spain with Catalonia's ex-leader Carles Puigdemont.
She posted on social media she had resumed working at the University of St Andrews in Fife.