An unprecedented data leak has laid bare how at least a dozen world leaders have been using tax havens to hide their wealth.

Millions of documents obtained from the server of a law firm based in Panama that specialises in setting up offshore companies reveal links to 72 current or former heads of state, including dictators accused of looting their own countries, it was reported last night.

Dubbed the Panama Papers, the leaked files show how some of Vladimir Putin’s closest allies have been channelling millions of pounds through offshore companies.

The Russian president has previously called for the “deoffshoreisation” of the country’s economy to reverse a trend of firms being registered in tax havens. Other national leaders revealed to have offshore assets include Nawaz Sharif, the Pakistani prime minister, Ayad Allawi, the former vice-president of Iraq, and Petro Poroshenko, the president of Ukraine.

Gerard Ryle, director of the International Consortium of Investigative Journalists (ICIJ), said the documents covered the day-to-day business at Mossack Fonseca, the fourth biggest offshore law firm, over the past 40 years.