Pakistan's Supreme Court has struck down a new law designed to exempt top government officials from contempt of court charges. Five judges, headed by Chief Justice Iftikhar Mohammed Chaudhary, said that granting immunity to public office holders was unconstitutional.

The ruling could see PM Raja Pervez Ashraf thrown out of office. His predecessor, Yousuf Raza Gilani, was removed by the court after he was convicted of contempt. The court wants the government to write to the Swiss authorities asking them to reopen an old corruption case against President Asif Ali Zardari.

Mr Gilani refused, arguing that the president had immunity from prosecution as head of state.

It is believed that the new contempt law was introduced to prevent the court from disqualifying Mr Gilani's successor.

The court has given Mr Ashraf until 8 August to write the letter to Switzerland. If he fails to do so, he could face the same fate as Mr Gilani.

The corruption case dates back to the 1990s when Mr Zardari and his late wife, former Prime Minister Benazir Bhutto, were accused of laundering millions of dollars in kickbacks in Swiss bank accounts. Mr Zardari says the charges are politically motivated.

The wrangling between the court and the government is part of a long and bitter feud. The government also has a troubled relationship with Pakistan's powerful military.