There are options for Syria, but none of them is attractive nor likely to be conclusive.

We can continue with the diplomatic efforts of the United Nations, but the obduracy of Russia and China in the Security Council, and the overt support for Assad from Moscow, stand firmly in the way of progress. When Kofi Annan, UN special envoy to Damascus, stood down, two questions were asked. Who can bring a peaceful solution to Syria if Kofi Annan cannot, and who would even want to try? The second question has been answered by the appointment of Lakhdar Brahimi, a UN servant of almost the same distinction as Annan. But if he can succeed it will be nothing short of miraculous.

The option that is most often publicly canvassed is "intervention", loosely used in furtherance of the dangerous principle "that something has to be done". But Syria is not Libya. In spite of the strengths of the insurgency, and even recent high level defections, the Assad regime is still supported by the Syrian political and military elite. Intervention on the Libyan model would be hazardous, but there is a more fundamental problem. Without any express mandate from the UN, few countries, if any, would be willing to commit. Any such action would require the participation or at least the active support of the United States. In the year of a presidential election, neither incumbent Obama nor challenger Romney would be willing to advocate yet another foreign adventure.

But there is one option which is being pursued now – covert intervention. Logistical support, intelligence, and communications can all be made available, and have the virtue of being deniable. For the moment that, allied to a hope and a prayer that Brahimi might succeed, is as good as it is going to get.

Assad is not strong enough to stamp out the insurgency and the insurgents are not strong enough to bring him down. Not checkmate but stalemate.

Sir Menzies Campbell is former leader of the Liberal Democrats