Deputy prime minister had been due to argue case for a change to 'new and better' voting system at Lib Dem's yes to AV launch

Nick Clegg has pulled out of the launch of the Liberal Democrats' yes to AV campaign launch to attend an emergency cabinet meeting on Libya.

The deputy prime minister was planning to defy calls for him to "lie low" in the referendum for voting system reform by speaking at the launch of the Liberal Democrats' yes to AV campaign launch in Manchester on Friday, which will now go ahead without him.

Clegg was forced to ditch his plans as the cabinet met to prepare plans to protect the Libyan rebel stronghold of Benghazi after the UN security council voted in favour of a no-fly zone and air strikes against Muammar Gaddafi's forces.

The Liberal Democrat leader was billed to argue the case for a change to a "new and better" voting system "with passion". The alternative vote is not proportional representation and was described by Clegg before the general election as a "miserable little compromise", but it was the best the Lib Dems could secure in coalition negotiations with the Tories as a step change away from the first-past-the-post system.

The issue has drawn a dividing line between Clegg and David Cameron, who in line with the vast majority of his MPs is in favour of the existing system.

Labour is split on the issue, with many high-profile veteran MPs and peers leading a vocal no campaign at odds with Miliband's support for the change.

Clegg had prepared to cast the referendum as a battle "not between left and right" but between "reformers and conservatives".