By Sam Edwards
BARCELONA, Spain (Reuters) - Catalonia will declare independence from Spain within 48 hours if voters back secession in an October referendum, according to a draft bill proposed by secessionist parties on Tuesday, though it remains unclear whether the vote will go ahead.
Spain's Constitutional Court and the conservative government in Madrid have blocked previous secessionist challenges and the government has said it will block any further attempt to hold a referendum.
According to the bill, written jointly by the parties which favor secession, the referendum will pose a binary question asking voters whether they want Catalonia, a wealthy region in northeastern Spain, to become an independent nation.
If "Yes" wins, the regional government plans to declare independence within 48 hours. If "No" wins, an early election would be called to form a new regional government.
The bill establishes no minimum participation for the referendum's outcome to be valid.
In 2014, Catalonia held a non-binding election on whether the region should be independent despite pressure from Madrid. While more than 80 percent agreed, turnout was low, at around 2.2 million out of 5.4 million potential voters.
Catalonia's regional government has said that while details of the bill will be debated in the coming weeks, a formal draft will not be sent to the Catalan legislature until August in an effort to forestall the Constitutional Court blocking the legislation.
The bill's announcement comes at a difficult time for the regional government led by Carles Puigdemont.
On Monday Puigdemont fired a senior member of his government for expressing doubt over the viability of plans to hold the referendum, highlighting tensions between different elements of the governing pro-independence coalition.
The Catalan government also faces technical challenges and has so far been unable to secure ballot boxes for the planned referendum.
(Editing by Angus Berwick and Gareth Jones)