Cameron puts proportional representation on the table but insists he wants to keep first past the post

This morning's Tory press conference was all about wooing LibCon waverers. "The Guardian wing of the Conservative Party" was how Nick Watt described the conference's emphasis on the environment, civil liberties, localism and education - as represented by Greg Clark, Dominic Grieve, Caroline Spelman and Michael Gove.

But if CCHQ wanted to talk about these issues the press only wanted to talk about proportional representation. Four times Mr Cameron was asked to rule out a PR deal with Nick Clegg but four times he refused. He attacked PR persuasively - and conceded that first past the post needed reform in the form of fairer seat sizes - but declined to give a pledge that he would keep FPTP in the event of a hung parliament.

Earlier, on Radio 4's Today programme, Iain Duncan Smith had argued that PR would not be an acceptable price of any hung parliament negotiations. Charles Kennedy had argued that PR was "a bottom line" for his party.

A ConservativeHome poll in February found 86% of members unwilling to accept PR as the price of a deal with the Liberal Democrats.

Tory strategists think a pledge to hold a referendum on electoral reform will be unavoidable if the Tories need Nick Clegg's support in the next Parliament.

Tim Montgomerie