Rehman Malik, the former second-most senior police officer in Pakistan, stands accused not only of unwarranted vilification of the prime minister, but also of abusing his official position.

Mr Malik's 200-page report formed the basis of corruption allegations published in a London newspaper, The Observer, last Sunday.

The paper claimed that a five-year investigation into Mr Sharif had revealed that he had massive hard currency assets abroad and had failed to declare some of them in the manner required by Pakistani law.

Mr Malik is currently thought to be in London.

'Vilification campaign'

The opposition Pakistan People's Party (PPP) says police started investigating Mr Sharif's assets before he came to power. But, they say, when he started his current term as prime minister the official investigations were effectively stopped.

The BBC's Owen Bennett-Jones: Bolstering the views that the whole ruling establishment is riddled with corruption

Mr Malik sent all the relevant material to the Pakistani President, Rafiq Tarar.

But a spokesman for the president dismissed the report as part of an unwarranted vilification campaign against the prime minister.

The opposition in Pakistan has been trying to secure a parliamentary debate on the corruption charges, but has so far been rebuffed.

It says it will try again in the Senate, where the government is weaker.

No comment from Sharif

The prime minister has so far declined to comment on the charges against him.

Allegations mirror those made against the Bhutto family

But many government loyalists have been defending him, describing the allegations as an attempt to divert attention from the corruption charges faced by the PPP leader, Benazir Bhutto.

The Sharif family threatened legal action immediately after The Observer accused Mr Sharif of large-scale corruption, but so far their response has been limited to lodging a written protest with the Press Complaints Commission in London.

The protest accused The Observer of trying to undermine and destabilise the democratic process in Pakistan by publishing baseless stories.