In other words, if Cameron doesn't like the membership rules, tough.
He can hold a referendum if he wants, and leave the EU if he wins, but there's no way he can get the other 27 members to change the basic rules of the organisation just to solve his little political problem at home.
In fact, Merkel will even try to ensure that Cameron loses next year's British election so that there is no referendum on Britain's EU membership. Being an experienced politician, however, Merkel delivered that part of her message in a deniable way.
It was officials from Merkel's own office and the German foreign ministry who briefed the newsmagazine Der Spiegel on her plans in that regard. They were not to be quoted by name - and it was left to the rest of us to figure out what her words would do to Cameron's re-election chances.
Cameron has recently been talking about imposing "quotas" on low-skilled people from other EU countries moving to Britain in a desperate attempt to get around the EU rules.
"Should Cameron persist in this quota plan, Chancellor Angela Merkel would abandon her efforts to keep Britain in the EU," Merkel's officials told Der Spiegel. Merkel has launched a counter-strike that may well bring Cameron down.
By making it crystal clear that his "re-negotiation" strategy cannot work, she is effectively telling British voters that if they re-elect Cameron's Conservatives in the election that is due next May, they will be voting to leave the EU.
The election itself becomes a referendum on EU membership - a referendum which she obviously thinks he will lose.
She is probably right. For all the fulmination in the British right-wing press about the country being overrun by immigrants from poorer EU countries, public support for EU membership in Britain is higher than it has been since 1991.
It is still only a modest 56 per cent, but that is a lot higher than the 44 per cent support that the same Ipsos MORI polling organisation found only two years ago.
This would normally be to the advantage of the Conservative Party, whose own right-wing "backwoodsmen" share these views.
In normal times, when the grown-ups are in charge, the party harvests these votes each election while never intending to do anything so foolish economically as to actually quit the EU.
Cameron belongs to the grown-up majority in the Conservative Party, and is not personally anti-EU. But the emergence and explosive growth of the United Kingdom Independence Party (UKIP), specifically tailored to appeal to the anti-immigrant-and-EU vote, has panicked the right wing of the Conservative Party.
Cameron has had to move further and further right to placate them and compete with UKIP, so he can no longer afford to be sensible about the EU. Merkel has understood this, and has effectively written him off even though she is a conservative herself. Her strategy now is to force Cameron into an openly anti-EU stance, split the right-wing vote in Britain evenly between the Conservatives and UKIP, and open the way for Labour to win the election.
Because that's the only way she can see to keep Britain in the European Union.
Gwynne Dyer is an independent journalist whose articles are published in 45 countries.
