The Deputy Prime Minister has laid bare a major coalition rift by revealing that he wants David Cameron to launch an investigation into the Culture Secretary Jeremy Hunt's handling of the BSkyB bid.
Nick Clegg has repeatedly told Mr Cameron that the independent adviser on ministerial interests, Sir Alex Allan, should be brought in to consider the case.
The Liberal Democrat leader has signalled that his MPs will abstain in Wednesday's vote on the issue, which is being forced by Labour.
The Commons motion calls for Sir Alex to investigate whether Mr Hunt, who is a Conservative, misled Parliament and failed to take responsibility for his special adviser Adam Smith, who resigned after admitting his contacts with News Corporation had been too close.
The Lib Dem decision was said to have received "unanimous support" at a meeting of the parliamentary party last night.
The difference of opinion in the coalition is likely to increase pressure on the Prime Minister to call in Sir Alex for an independent assessment of whether the ministerial code was breached.
Labour is unlikely to win the Commons vote on Mr Hunt, despite the Lib Dem abstention.
Even if the motion is passed it would only be a symbolic blow to Mr Cameron, as he retains the final say over whether his independent adviser investigates a minister.