HALF a million Catalans have signed up for what organisers claim will be Europe's biggest ever pro-independence rally tomorrow.

All have registered for the rally which will take place along two of the main avenues in Barcelona to form a perfect "V" for Victory, Vote and Voluntat - or Will - from the sky.

The protest comes as Madrid issues increasingly stern warnings that it will attempt to block a Scottish-style independence referendum scheduled for November 9.

Spanish Prime Minister Mariano Rajoy earlier this week said he had unspecified measures in place to stop the vote - which, unlike Scotland's, is not legally binding, and deemed unconstitutional by unionists.

The symbolic half-million figure is higher than a figure of 455,000 registered for a rally this time last year also timed to coincide with Catalonia's La Diada national day.

The Catalan National Assembly, the grassroots organisation behind the "V" or Via Catalana protest, expects more people to turn up on the day.

Nationalists are split on how to react if the vote is blocked. Opposition leader Oriol Junqueras, of Esquerra Republicana, the left-wing formal ally of the SNP, favours civil disobedience. Artur Mas, the pro-independence centre-right president of Catalonia, does not.