The European Union must prepare itself for the breakup of countries within its frontiers, the regional prime minister of Catalonia warned on Thursday, adding that Madrid could not simply ignore a huge independence demonstration held in Barcelona this week.

Artur Mas said: "Europe will at some time have to think about this. It wouldn't make sense if, because of some rigid norms, it was unable to adapt to changing realities."

His comments came after the European commission president, José Manuel Barroso, indicated this week that any new state would have to apply to join the EU.

Mas said there would be no looking back for Catalonia after the march, which police said was attended by 1.5 million people – a fifth of the population of the north-eastern region. He also warned the Spanish prime minister, Mariano Rajoy, and his conservative People's party (PP) government that they would be foolish to try to ignore the apparent desire for greater autonomy.

"This was not a sudden summer fever," he said. "In Barcelona there was a vast, peaceful multitude of people … The biggest possible mistake would be to minimise what is happening.

"It was very important both quantitatively and qualitatively. The feeling was that Catalonia cannot continue on the current path, that it needs its own project."

His words came as the state television company, TVE, apologised for relegating the demonstration to fifth place in its evening news, a move that underlined the growing disconnection between Madrid and Barcelona. "This news item was poorly placed on the evening news," a spokesman admitted. "That was an error."

Mas, from the Catalan nationalist Convergence and Union coalition, suggested that independence was not the only solution. Many members of his regional government were at the march and his party is often accused of calculated ambiguity on the matter.

"I identify with the popular outcry," he said, adding that only his responsibilities as regional prime minister had prevented him from joining the demonstrators. "Catalonia needs a state," he added. "For years we thought it could be the Spanish state."

But just as northern Europe was getting fed up with the south, and vice versa, so Catalonia and the rest of Spain were now fed up with one another, Mas said.

He implied that one way for Rajoy to dampen the surge in separatist feeling would be to agree to a change in funding, allowing Spain's wealthiest region to hold on to more of the tax it generates.

Catalonia wants to be able to collect its own taxes and send a share to Madrid, rather than the other way around. That would make it different from most of Spain's other 16 regional government, but similar to the northern Basque country.

Mas will see Rajoy next week to discuss what he called an issue of "fiscal sovereignty". Popular outrage at Catalan money going elsewhere amid health and education cuts was fuelling the thirst for independence, he suggested.

Mas said that whatever changes came after this week's demonstration, Catalans wanted to stay in the EU and the euro. "We haven't gone mad," he said.

Catalonia enjoys a high degree of self-government, running health, education and local policing, but allowing it to form a separate state would be both extremely difficult and potentially explosive. A legal separation would require a change in the Spanish constitution and approval by voters in other parts of the country in a referendum – which seems unlikely.

"Unilateral secession does not fit in Spain's constitutional framework," foreign minister José Manuel Garcia-Margallo declared on Thursday. "A declaration of independence by a region does not fit."

Officials in Brussels have also said that Catalonia would automatically leave the EU, and might have to abandon the euro and print its own currency.

"A new state, if it wants to join the European Union, has to apply to become a member like any state," Barroso said this week. "And all the other member states have to give their consent."

Garcia-Margallo warned that Catalonia or any other Spanish region that achieved independence would find itself at "the back of the queue" for joining the EU.

The independence demonstration sets a further challenge for Rajoy as he copes with 25% unemployment and a double-dip recession, and decides whether to request a bailout by the European Central Bank and fellow eurozone countries.

"Catalonia has serious deficit and employment problems and this is not the moment for messing around," Rajoy said before the demonstration.

Mas's government has launched several austerity programmes as it struggles to bring down its deficit, and ratings agencies give its debt junk status.

Economists doubt it will hit deficit targets set by the central government this year, however, and Rajoy's government – which is keen to persuade fellow eurozone countries it can control overspending regional governments – has threatened to intervene and take direct control of regional finances where that happens.

Mas has threatened to call elections if that is done in Catalonia, believing it would provoke a wave of nationalist sentiment. Catalans pay between ¤12bn and ¤16bn more in taxes each year to Madrid than they receive back, with the excess going to poorer regions such as Andalusia and Extremadura.