About a million people have gathered in Barcelona to renew their calls for Catalan independence and to demand the release of jailed political leaders almost a year after the unilateral referendum that triggered Spain’s worst political crisis since its return to democracy.

The annual Diada celebrations commemorate the fall of the city at the end of the Spanish war of succession in 1714, but in recent years they have been used by pro-independence groups as a show of strength.

The issue of independence remains divisive in the region, with polls suggesting Catalans are almost evenly split on whether to stay part of Spain.

Organisers said 460,000 people registered to take part in the rally, while police in Barcelona put attendance at about 1 million, making it roughly the same size as last year’s event.

Once again, the independence movement demonstrated its extraordinary capacity to mobilise its base, filling about four miles of Diagonal, the city’s broadest street, with hundreds of thousands of flag-waving supporters dressed in T-shirts bearing the slogan: “We’re making the Catalan republic”.

With chants of “the streets will always be ours” and “independence”, the massive crowd assembled rather than marched in their allotted sections along the street.

Then at 17:14 – to correspond with the year that Barcelona fell – there was silence, followed by a wave of sound that roared from one end of Diagonal to the other, where it symbolically toppled a wall representing direct rule that Madrid imposed for several months after the independence declaration last October was ruled unlawful.

In a sign of the divisions in Catalan society, two of the main anti-independence parties boycotted Tuesday morning’s wreath-laying ceremony at the statue of Rafael Casanova, hero of the defence of Barcelona before it fell.

Citizens, the single largest party in the Catalan parliament, and the smaller People’s party stayed away while the Catalan Socialist party (PSC) withdrew from the Diada’s institutional events for the first time this year, arguing that the annual celebration had become one that excluded half of Catalonia’s population.

Barcelona’s mayor, Ada Colau, attended the wreath ceremony but said she would not take part in the march because it explicitly demanded independence and therefore only represented half of Catalans. “As mayor I have a duty to seek consensus,” she said.

Facebook Twitter Pinterest The Catalan regional president, Quim Torra (second right) attends a ceremony at the tomb of Rafael Casanova in Barcelona province. Photograph: Quique Garcia/EPA

On the eve of the Diada, Catalonia’s president, Quim Torra, said he intended to press on with plans to deliver the sovereign republic that was unilaterally declared last October by the government of his predecessor Carles Puigdemont.

The declaration prompted the Spanish government to sack Puigdemont – who fled to Belgium – take direct control of Catalonia and call a snap regional election. Several Catalan politicians, including Puigdemont, remain in self-imposed exile; others are in prison in Spain awaiting trial for their roles in the push for independence.

“This is not just about Catalan independence, it’s a struggle for basic rights and freedom of expression in Spain,” said Torra on Tuesday, citing the case of the rapper Valtònyc who was sentenced to three and a half years in prison for songs that threatened a politician, glorified terrorism and insulted the crown.

While the socialist government of Pedro Sánchez has taken a less confrontational line on the Catalan crisis than the conservative administration it replaced in June, it has said negotiations must be conducted in accordance with the constitution, which stresses the “indissoluble unity of the Spanish nation”.

Sánchez, who met Torra in July, has offered a vote on greater Catalan self-government, but has firmly ruled out a referendum on either self-determination or independence. He has also warned that any unilateral attempts to create an independent Catalonia will result in the re-application of direct rule from Madrid.

“Pedro Sánchez talks about self-government but what we’re interested in is self-determination. So far we can agree on the ‘self’ bit,” Torra said, adding that “at least Sánchez is looking for a political solution”.

He denied Catalan society was divided on the issue, despite the secessionist parties never having achieved more than 48% of the popular vote. “We are all united behind the Catalan republic,” he said.

Independence campaigners have promised a “hot autumn” of protests and mass mobilisations in the run-up to the trials of the imprisoned leaders. However, recent months have laid bare the divisions between the main pro-independence parties.

Observers and analysts point out that the plight of the Catalan prisoners remains the key bar to the progress of further negotiations. On Tuesday, Spain’s foreign minister, Josep Borrell, said he would personally have preferred to see them released on bail.

Pablo Simón, a political scientist at Carlos III University in Madrid, said the independence movement would not give ground as long as many of its leaders were in jail. That “resistance-style” mentality, he added, would favour the interests of those agitating for a return to unilateral action and create further divisions with more moderate elements.

“The problem is there’s no road map,” he said. “In order to have one, they’d need leadership, and because there’ll be no leadership as long as the tensions continue, the independence movement runs the risk of becoming paralysed.”

Oriol Junqueras, the leader of the Catalan Republican Left (ERC) party who served as Puigdemont’s vice-president and has been in prison since November, warned there were no shortcuts to sovereignty.

“You need to have the courage to speak clearly if you’re going to move ahead,” he told Catalan TV on Monday. “You have to admit where we are and where we’d like to be. You have to start building again from there and learning from the mistakes that have been made.”