Leaders of Pakistan's ruling coalition are due to meet in London this week to resolve differences over how to reinstate judges dismissed in November by President Pervez Musharraf, officials said yesterday.

Strains over the issue within the month-old coalition, led by the party of assassinated former Prime Minister Benazir Bhutto, have raised speculation that the anti-Musharraf alliance could collapse, though party leaders have asserted their unity.

Western allies in the war on terrorism dread nuclear-armed Pakistan sliding into a prolonged period of instability. Critics fear the failure to move forward over the judges has diverted Prime Minister Yousaf Raza Gilani's government from more pressing issues like rising inflation, deteriorating trade and fiscal deficits and the fight against Islamist militancy.

Asif Ali Zardari, Bhutto's widower who succeeded her as leader of the Pakistan People's Party (PPP), will meet Nawaz Sharif, the leader of the second largest party in the coalition, after their aides failed to bridge differences over how to restore the judges.

Former Prime Minister Sharif, leader of the Pakistan Muslim League (Nawaz) is in London, where his wife is receiving medical treatment.

"I was leaving for Pakistan but Mr Zardari asked me to stay back for a meeting," Mr Sharif told private Geo television.

The two, neither of whom are members of the government or Parliament, met in Dubai last week for urgent consultations to break the log jam over the judges.