THE Spanish state adviser has backed a veto of a watered-down Catalan vote on independence planned for November 9, making it likely the government will try to have the "consultation of citizens" blocked by the courts.

Spain's Council of State has unanimously decided the government should ask the Constitutional Court to declare the vote illegal, a spokeswoman for the consultative body said.

Last month Catalonia dropped plans for a non-binding referendum on independence from Spain after the court declared such a vote unconstitutional.

Catalan leader Artur Mas instead announced plans for an alternative consultation on the same day, equally non-binding, and open to anyone who wants to cast their ballot. It will be marshalled largely by volunteers.

Spanish Prime Minister Mariano Rajoy had already threatened to try to have the "consultation of citizens" blocked if it were found to be illegal.

He said the cabinet would decide on the government's next move today.