Unofficial poll in days before coronation of Prince Felipe will ask Spaniards if they want an elected head of state

Emboldened by the tens of thousands of Spaniards who have taken to the streets to demand a say in the future of Spain's monarchy, activist groups have announced they will be holding their own referendum in the five days leading up to the coronation of Prince Felipe.

The idea came about on the night King Juan Carlos announced his abdication, after an estimated 20,000 people dressed in the red, yellow and purple of the former Spanish republic descended upon the Puerta del Sol square in Madrid calling for an end to the monarchy.

"It seems absurd to us that in a democracy nobody is asking the citizens if they want a monarchy or a republic," said Kike Castelló of ¡Democracia Real Ya! (Real Democracy Now!), one of the dozen or so collectives involved in organising the referendum.

The referendum will begin on Saturday morning and run until 19 June, the day of the coronation. About 60 polling stations staffed by volunteers will be set up along major streets in cities across the country, with voting also taking place online.

#ReferéndumRealYA. Estas son las preguntas que haremos entre los días 14 y 19 de junio. pic.twitter.com/zFEYltuKvA — #ReferendumRealYa (@Referendum1419) June 8, 2014

A recent poll for El País found that 62% of Spaniards believe a referendum on the monarchy should be held "at some point". Nearly half, said the poll, would prefer a monarchy headed by Felipe, while 36% would support a republic.

Participants will be asked to answer yes or no to two questions: whether they agree that the head of Spain should be elected and if they agree that a constitutional process should be opened so that citizens can decide how the Spanish state is governed.

"We just want people to express their opinion – whether it's for a monarchy or for a republic. We want to hear what Spaniards want for their country," said Castelló.

He brushed aside concerns about the legality of the referendum. "Asking people for their thoughts isn't illegal," he said, pointing to a line in the Spanish constitution that stipulates that "transcendent decisions can be put to a consultative referendum".

Under Spanish law, he added, permission is not needed for this kind of initiative. The only obligation is that those setting up polling stations notify the delegate from the central government in the region. The necessary forms are provided on the group's website, he said.

Measures are being put into place to avoid people voting more than once, said Eduardo Robles Elvira, who is working on the technical aspects of the poll. Independent organisations are being recruited to monitor and tally the results. "We're doing all of this so that it's the most transparent and legitimate referendum possible," he said.

The group has yet to decide what exactly they will do with the results, said Castelló. "We know that the government isn't going to say, 'hey, look how many people want a republic, let's do that." He said he saw the effort to take the pulse of the streets as more symbolic than anything else. "We want people to realise that it's possible for us to have a say in how our country is run."

The plebiscite is open to Spaniards living anywhere in the world, and a group in Paris has signed up to host a polling station on the streets of the French capital. "Spaniards are the ones who will be affected by this monarchy. If you want one as well for the British, we can organise one for your Queen," Castelló joked. "But that might seem a bit weird."

MPs in the Izquierda Plural party demonstrate in parliament in favour of a referendum during the abdication debate. Photograph: Pablo Blazquez Dominguez/Getty Images

More than 85% of the Spanish parliament on Wednesday voted to move forward with the law that will pave the way for the crown to be handed from King Juan Carlos to Prince Felipe. The law will now move to the Spanish senate where it is expected to be approved early next week.

As leftist deputies waved signs calling for a referendum, Mariano Rajoy, the prime minister, defended the monarchy during the debate, saying: "Spain is a parliamentary monarchy with deep roots because Spaniards want it to be so."