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Four of the imprisoned pro-independence Catalan leaders were elected late last month to Spain's CongressOriol JunquerasJordi SànchezJordi Turull and Josep Rull. All four have asked the presiding judge in their case, Manuel Marchena, to allow them to attend the opening of parliament on 21st May to collect their certificates of election. Given this exceptional prospect, police at the Madrid chamber, part of the National Police Corps, are already working on the necessary procedures. Their main aims are discretion and to avoid images of the four in handcuffs. As of yet, no meetings have been held with the interior ministry and the Supreme Court hasn't yet evaluated the petition.

According to Congress sources, they will be transported from Soto del Real prison by the Civil Guard, who will then hand them over to the National Police Corps. This is the same procedure followed on days when the trial at the Supreme Court is in session. They would enter the chamber through the underground car park, taking the elevators up into the building, passing through the police office. "Common sense says the least fuss possible must be made," the sources say.

For the National Police Corps, this means avoiding images of the prisoners in handcuffs, which could affect their dignity. To remove their shackles, however, would require either an explicit order in writing from judge Marchena, or a decision from the chamber's acting speaker, Ana Pastor, in charge of the police within the building.

Within the chamber, there will be the normal security team present, according to the draft plans. "It's a very protected place. It's impossible for them to escape," the sources say.

There is also a political decision to made as to their location within the chamber during the ceremony, when the parliamentary parties still don't have their seats assigned.

Overall, according to the sources: "We're working on it. We haven't spoken with the interior [ministry] yet, nor do we have any idea when we'll do so. From the operational point of view, it's very quick to set up: one day is enough".

As well the four imprisoned pro-independence leaders elected to the Spanish Congress on April 28th, a fifth jailed defendant in the trial, Raül Romeva, was elected to Spain's Senate.