The 'Panama Papers' revealing how the rich and powerful use tax havens to conceal their wealth illustrate the need for reforming the system, according to Christian Aid.

More than 11 million documents were leaked from Panamanian law firm Mossack Fonseca. The papers cover a period over almost 40 years, from 1977 until last December, and appear to implicate many of the world's richest and most powerful people.

They allegedly show that some companies domiciled in tax havens were being used for suspected money laundering, arms and drug deals and tax evasion.

"I think the leak will prove to be probably the biggest blow the offshore world has ever taken because of the extent of the documents," said Gerard Ryle, director of the International Consortium of Investigative Journalists.

Among those involved are 12 current or former heads of state and 61 people linked to current or former world leaders, including close associates of Russian president Vladimir Putin.

Mossack Fonseca has denied accusations of wrongdoing.

According to Christian Aid, which has campaigned for the reform of international taxation regimes because of the amount of money lost to the governments of poor countries, the revelations have "exploded any remaining excuses the UK had for allowing secrecy in its tax havens".

The British Virgin Islands are the most popular location for the companies exposed in the Panama Papers as existing to facilitate huge financial transactions.

The UK is second only to Hong Kong as the host of the banks and law firms which have facilitated the enterprise.

"This leak exposes the extent to which UK tax havens and UK-based intermediaries are at the very heart of this rotten system," said Toby Quantrill, Christian Aid's principal economic justice adviser, in statement sent to Christian Today.

"David Cameron will host a major anti-corruption summit next month and the Panama Papers have exploded any remaining excuses the UK had for tolerating secrecy in the many tax havens it controls – the British Virgin Islands, Caymans and Bermuda among them. The Prime Minister has a month to sort this out if he wishes to host this anti-corruption conference without his credibility being called into question."

Research by the Tax Justice Network indicates that the UK and its Overseas Territories and Crown Dependencies are together the world's largest tax haven.

Quantrill said: "The Prime Minister has the power to clean up a major chunk of the global financial system, and in the light of the Panama Papers, he should use it. The UK must take immediate steps to reveal the real owners of business in the territories that we control so the public can know the truth."

He added that the UK "simply cannot continue to provide cover for the rich and powerful who wish to operate in the shadows".