Hundreds of thousands of pro-Spanish unity supporters marched through the streets of Barcelona on Sunday, exactly a week after voters in a banned referendum in Catalonia voted overwhelming in favour of breaking away from Spain.

The massive pro-Spain march, which passed off without incident, ran under the slogan “For the restoration of seny” – the Catalan word for common sense or folk wisdom.

The organisers of the march, the pro-unity association, the Societat Civil Catalana (SCC), later claimed nearly a million pro-unity supporters had turned out. That figure was disputed by the local police force, who estimated the demonstrators at the still very significant total of 350,000.

While Spanish premier Mariano Rajoy did not attend but expressed his support in a tweet, a number of heavyweights from the ruling Partido Popular, including the president of the Madrid region, Cristina Cifuentes, took part. Also present was Albert Rivera, leader of Spain’s fourth largest party, Ciudadanos, and the Nobel-winning author Mario Vargas Llosa.

In a reflection of the divisions within the pro-unity camp, though, only a few top members of Spain’s leading opposition party, the Socialists, participated, the most prominent being Josep Borrell, a former president of the EU. As for Spain’s hard-left Podemos party, its leader Pablo Iglesias was roundly booed by some 50 pro-unity demonstrators when he was spotted at Barcelona Sants railway station early this morning – catching a train for Madrid.

In a manifesto read at the end of the demonstration, there were demands that non-nationalist Catalans “should not be marginalised” and Mr Vargas Llosa launched a stinging attack on the nationalists, accusing their leaders, among them regional premier Carles Puigdemont, of being golpistas – conspirators in a coup d’état. “The nationalist plot will not destroy 500 years of Spanish unity,” he insisted.

The march came just two days before Mr Puigdemont is expected to make a key address to the Catalan parliament, which opposition sources have reportedly claimed will see him make a unilateral declaration of independence.

“He should not do such a senseless, provocative thing,” Jose Domingo, vice-president of the SCC, said during the demonstration.

Mr Domingo’s comments echoed Spanish PM Mariano Rajoy’s words on Sunday, when he hinted strongly in an interview he was considering using Article 155 of the constitution, which allows for direct intervention from Madrid, should an independence bid happen.

Speaking to El País in his first full-length newspaper interview since last Sunday’s banned referendum sparked Spain’s worst political crisis in 40 years, Mr Rajoy said “[Catalan] independence is not going to happen.”

Asked specifically about article 155, Mr Rajoy answered: “I am not ruling out anything that the law says.”

“Ideally, we should not have to resort to drastic solutions, but in that case there would have to be rectifications.”

Mr Rajoy also promised that both the Civil Guard and the Spanish national police would remain in Catalonia “until things return to normal”.

Today’s massive pro-unity demonstration and Mr Rajoy’s uncompromising stance are not the only external pressures Mr Puigdemont faces in the countdown to a possible declaration of independence. This week senior Catalan business executives have met the regional premier to urge him to cancel the declaration.

Catalonia referendum protests – in pictures Show all 10 1 /10 Catalonia referendum protests – in pictures Catalonia referendum protests – in pictures Demonstrators block a Guardia Civil vehicle as they try to leave the Department of External Affairs, Institutional Relations and Transparency of the Catalan Government office in Barcelona AP/Emilio Morenatti Catalonia referendum protests – in pictures Demonstrators react as they try to stop the car carrying Xavier Puig, a senior at the Department of External Affairs, Institutional Relations and Transparency of the Catalan Government office, after he was arrested by Guardia Civil officers in Barcelona AP/Emilio Morenatti Catalonia referendum protests – in pictures A demonstrator reacts as he tries with others to stop the car carrying Xavier Puig, a senior at the Department of External Affairs, Institutional Relations and Transparency of the Catalan Government office, after he was arrested by Guardia Civil officers in Barcelona AP/Emilio Morenatti Catalonia referendum protests – in pictures Spokeswoman of the Catalan pro-independence anticapitalist party "Candidatura d'Unitat Popular - CUP" (Popular Unity Candidacy), Ana Gabriel, talks to the media in Barcelona Josep Lago/AFP Catalonia referendum protests – in pictures Republican Left of Catalonia party's (ERC) Member of Parliament Joan Tarda (C) attends a demonstration outside the regional Economy Ministry in Catalonia during a police search for documents connected with the organisation of the Catalan independence referendum, in Barcelona EPA/Alejandro Garcia Catalonia referendum protests – in pictures A man holds pro-referendum poster next to a Spanish Civil Guard who stands in front of the Economy headquarters of Catalonia's regional government in Barcelona. The operation comes amid mounting tensions as Catalan leaders press ahead with preparations for an independence referendum on October 1 despite Madrid's ban and a court ruling deeming it illegal Josep Lago/AFP Catalonia referendum protests – in pictures People hold placards reading "Democracy" as they protest in front of the Economy headquarters of Catalonia's regional government in Barcelona AFP Catalonia referendum protests – in pictures A crowd of protesters gather outside the Catalan region's economy ministry after junior economy minister Josep Maria Jove was arrested by Spanish police during a raid on several government offices, in Barcelona Reuters/Albert Gea Catalonia referendum protests – in pictures People holding 'Esteladas' (Catalan pro-independence flags) attend a protest near the Economy headquarters of Catalonia's regional government Lluis Gene/AFP Catalonia referendum protests – in pictures People demonstrate on a Spanish Civil Guard Police car outside the Catalan Vice-President and Economy office as police officers holds a searching operation inside David Ramos/Getty Images