A walk through the streets of Madrid or Barcelona provides even the most casual observer a clue as to the new face of Spain: Bolivian nannies, an Ecuadorian man clutching a hardhat, a Romanian mother chatting on her mobile.

In a market that has more bank branches per capita than any in the world, the immigrant population, which has mushroomed from fewer than 1m to at least 4m since 2000, holds the rare promise of new customers.