It would enhance his bargaining power, while the Tories can remind him that they allowed a vote on AV.
The combined attacks by the Lib Dems and Labour are further weakening public support for Gove's project.
The party's visceral attacks on the Lib Dems show it is staking everything on a majority.
The inclusion of the party would help to split the left-wing vote and harm Labour and the Lib Dems.
The party is determined to deny Clegg the chance to make a fresh appeal.
Rather than preparing for another hung parliament, Labour is focused on "crushing" Clegg's party.
Labour has a 16-point lead over the Tories, with the Lib Dems in fifth place behind Ukip and the Greens.
Cable has previously suggested that the coalition could end early, a demand now made by the Lib Dem peer.
With the general election result so uncertain, leadership contenders in the Tories, Labour and the Lib Dems are making themselves known.
Party writes to Jeremy Heywood asking whether Coetzee's involvement in Lib Dem election strategy has breached the special advisers' code of conduct.