Benazir Bhutto's husband is claiming the right to basic principles of fairness accorded by the UK legal system, reports Roger Pearson

Benazir Bhutto's husband is launching a High Court challenge in the wake of the Government's agreement to assist its Pakistani counterpart in investigating drug-trafficking allegations against him.

Mr Justice Latham has granted leave for Asif Ali Zardari to seek a declaration that he is entitled to see a letter from Pakistan which triggered the investigation. Zardari claims that the investigation is politically-motivated.

While the judge gave consent for Zardari to seek that declaration, he refused to give him the green light to challenge Home Secretary Jack Straw's agreement to a request from Pakistan for an investigation.

Counsel for Zardari, Lord Lester QC, claimed there was a "serious risk of injustice" unless sufficient information was provided to enable Zardari to benefit from the safeguards provided in UK legal proceedings. "This should not depend on the Pakistani government's wishes but on basic principles of fairness," he told the judge.

Zardari, a Pakistani senator, was placed under arrest in Pakistan in 1996, shortly after his wife had been removed as president. He was later charged in connection with the murder of his wife's brother, Murtaza, and also with corruption and evasion of customs duty.

He argues that the Home Secretary's decision to grant assistance to the Pakistani government was not based on those charges, but on the Pakistani government's confirmation that he also faced drug-related proceedings in Pakistan.

Mr Justice Latham was told that Benazir Bhutto and Zardari took the view that Pakistan's request for assistance was "part of a wider politically-motivated campaign" being waged by the Muslim League against the Bhutto family and the Pakistan People's Party, led by Bhutto.

Lord Lester said Zardari wanted access to the letter to give his lawyers an opportunity to cross-examine witnesses.

The judge agreed that there was an "arguable case" as far as the letter was concerned. Zardari's solicitors, Goodman Derrick have said that they will be asking magistrates dealing with the matter to keep police investigations on hold pending the full hearing in March.