Catalan separatists are finalising a deal for ousted leader Carles Puigdemont to hand over the presidency to an alternative candidate at home, while retaining a symbolic role from his exile in Belgium.

Under the plan, Mr Puigdemont would be symbolically inaugurated as the “legitimate president” before stepping aside for a day-to-day leader who can form a government and restore Catalan autonomy after four months of direct rule.

Independence parties said on Tuesday that they would vote through a parliamentary resolution establishing Mr Puigdemont’s status in a session scheduled for Thursday, prompting threats of court action from unionist opponents.

The Spanish government reacted with dismay to widespread reports that the likely alternative would be Jordi Sanchez, who has been in prison since October over his role in leading street protests as head of the grassroots Catalan National Assembly (ANC).

Rafael Catalá, the justice minister, said that just as a Catalan president who is “fugitive from justice and outside Spain” was “unimaginable”, so too it was “difficult” to conceive of a president “who is in prison and cannot exercise his functions”.