Cameron can't afford to stay silent on Europe
Michael Howard's intervention in the EU referendum debate sends an uncomfortable warning to David Cameron - your policy of having no policy cannot hold.
The policy in question is whether cabinet ministers should be free to campaign for Britain to leave the European Union if David Cameron eventually decides we should stay.
Downing Street might reasonably argue that since the referendum could be two years away - it is promised by the end of 2017 - it doesn't need to make a decision now.
If that is the belief in the prime minister's circle, it is naive.
Mr Cameron's renegotiation is expected to be completed in time for the next meeting of the European Council (the heads of government) in February.
As soon as that is done, cabinet ministers will come under tremendous pressure to say what they think of the deal.
The first expression of lukewarm support from one of David Cameron's colleagues risks quickly being interpreted as a leadership crisis.
Mr Cameron's advisers may see that as exactly the reason why cabinet ministers should not be allowed to campaign on the opposite side from the prime minister - it keeps them in line.
Yet, as Lord Howard observed when we spoke for The World This Weekend: "This is going to be a difficult time for the Conservative Party.
"It has always been a very divisive issue, not just in the Conservative Party but in other parties as well."
This is one issue on which an appeal to loyalty could fail; and if it did, Mr Cameron would look vulnerable.
The precedent is Harold Wilson's decision to allow his cabinet ministers to debate on both sides of the referendum on whether to remain in what was then the European Economic Community in 1975.
Wilson had tried and failed to impose a party line on Europe when the House of Commons debated joining in the first place. That led to a big rebellion by pro-Europeans and the resignation of Labour's deputy leader Roy Jenkins.
David Cameron may think that his general election victory against the odds entitles him to demand obedience from his ministers.
John Major was an election winner, too, but that didn't stop him experiencing the humiliation of serving ministers openly defying him during the 1997 election campaign.
A clutch of junior ministers made personal pledges never to join the euro even though Major's policy was negotiate first and decide later.
Lord Howard does impose a caveat on his proposal for cabinet ministers to enjoy freedom of conscience; it should apply only "when it comes to the campaign", he told me, and not before.
That was Wilson's rule, too. He informed the cabinet of his decision nearly six months before the referendum was held.
One for trivia buffs: there is an older precedent for cabinet ministers expressing contrary views.
According to Wilson's authorised biographer Philip Ziegler, Michael Foot told the prime minister that in 1932, the National Government, of which his father Isaac was a member, had allowed cabinet ministers to follow their own line over import duties.
That was a multi-party coalition; holding a single-party cabinet together ought to be easier, but David Cameron might be wiser not to take the risk.
Listen to the interview with Lord Howard on The World This Weekend.