41 arrests of nationals from six countries who allegedly have "numerous connections between groups of organised international crimes and a number of suspects implicated in Spain or abroad in serious criminal activities".

Illegally siphoned funds from Russia's crippled oil company Yukos had been discovered as part of the investigation, something the oil company has denied.

One of the key suspects is the head of the law firm, Fernando del Valle, 57, a Chilean citizen, who is said to have set up a network of property and front companies whose traces disappear into offshore accounts in the nearby British territory of Gibraltar, press reports said.

Some of the welter of documents seized by police since the weekend are understood to implicate an array of companies who have their fiscal base in Gibraltar. The tiny territory has just 30,000 residents but 80,000 companies.