Sharif was due to arrive at London's main Heathrow airport at 5:40 pm (1740 GMT) on a Saudi Airlines flight.

A spokesman for the opposition Pakistan Muslim League-Nawaz party said nearly 3,000 people were expected to head to Heathrow in west London to receive him. Britain has a sizeable Pakistani minority population.

Pakistani Information Minister Sheikh Rashid announced in November that Sharif would be issued with a passport so he can travel to London with his sick son.

Rashid said Sharif -- who was prime minister from 1990 to 1993 and again from 1997 until 1999 -- would be free to go anywhere, but that "he cannot come to Pakistan".

Industrialist-turned politician Sharif was ousted by General Pervez Musharraf in a bloodless coup on October 12, 1999. He was sentenced to life in prison on tax evasion and treason charges.