The First Minister of Catalonia, Carles Puigdemont, declared on Sunday evening that the only body that could now suspend his regional government from power was the Catalan Parliament, "the seat of popular sovereignty".

"There is no other court or political body that can do so", he said in his message to Catalans for the annual September 11 Diada Day celebrations.

He added that the new independence referendum, which his government has called for October 1, is legal "according to the laws of the Parliament of Catalonia" and that Madrid had rejected all of their efforts at dialogue.

Last week, Spain's Constitutional Court suspended the Catalan referendum law after accepting a central government challenge to its legality.

The public prosecutor has filed criminal charges against all of the members of Mr. Puigdemont's government and the Speaker of the Catalan parliament.

The leading Catalan separatist organisation, the ANC, said on Sunday that 400,000 people had now registered for Monday's big Diada Day protest, which this year will be a giant cross in the streets of central Barcelona, with participants all putting on a yellow t-shirt shortly before the key moment after 5 p.m.

Previous years have seen a giant "v", a human chain across the region or a large yellow triangular pointer, with the route organised around thematic spaces representing "democracy", "social justice" or "diversity".

The official slogan for this year's event is "the Diada of yes".

Shortly after Mr. Puigdemont published his message, the Deputy First Minister, Oriol Junqueras, appeared on an evening politics show to answer questions from the presenter and audience members.

Asked about what would happen if the Constitutional Court suspended him from office, he also argued, like the First Minister, that the only will he now represents is that of the Catalan people.

Mr. Junqueras said the highest law currently applicable in Catalonia was not the Spanish Constitution and statutes but "international law". He said there was no legal mechanism for Europe to eject a part of its territory and that Catalonia would continue to use the euro when it secedes.

On Thursday, European Parliament President Antonio Tajani said Catalonia must obey the Spanish Constitution and reiterated that if the region secedes it will be out of the European Union.

Some small territories have signed monetary agreements with the EU to be able to use the euro as an official currency, but only Kosovo and Montenegro use it without such a deal, as a de facto currency.

Last week, Spain's Deputy Prime Minister, Soraya Sáenz de Santamaría, said "democracy has died" in Catalonia.

The Prime Minister, Mariano Rajoy, promised Spaniards he would do what he saw as his duty and prevent the vote from happening: "There will be no self-determination referendum".

A second bill, related to the mechanics of secession, was also passed by the Catalan parliament, and will likely also be suspended by the Constitutional Court this week.