Egypt's highest court has ruled that Hosni Mubarak's last prime minister can stay in the presidential race and that a third of lawmakers in the Islamist-dominated legislature were illegally elected.

Thursday's ruling would allow Ahmed Shafiq to contest the presidential runoff on Saturday and Sunday against Islamist Mohammed Morsi despite a legislation banning old regime figures from running for office.

The second ruling arose from a lower court verdict that the principle of equality was breached when parties fielded candidates for the third of seats set aside for independents. Two thirds of the seats were contested by party slates.

The ruling means that elections must be held for a third of the seats. Parliament may be suspended until the new lawmakers are elected.