Threatening force against Assad would lead to an explosive stand-off with Russia and Iran, whilst bombing Isis in Syria now would represent a triumph of tactics over strategy. Only pro-active diplomacy can resolve this crisis.
For some time the Syria debate has revolved around whether or not UK military power should be deployed against Isis. This week, however, the focus seems to have shifted to the imposition of a no bombing zone, to be underpinned by the threat of using force against President Assad and/or the Russians.
That is grasping at tactical straws when the compelling need is for effective strategy.
In the absence of any clear view from Government, we are left to speculate about the pros and cons of the various options that are under discussion. The suggestion that the British navy could become engaged in the imposition of a "no bombing zone" (NBZ) has emerged very recently, but nobody has said clearly how it would work in practice. Thus far the NBZ proposal appears to be based on the threat of taking direct military action against Assad's forces if they were to violate the zones. Whether or not such action would also be taken against Russian assets entering the zones is unclear, but it has to be assumed that a no bombing zone would rapidly become a no credibility zone if the Russians were able to enter it with impunity.
Given the absence of detail around the NBZ, it would be wise to suspend judgement until a precise explanation of how it might work has emerged. However, it seems likely that such an approach would cause a dangerous ratcheting up of hostilities with Russia and Iran, leading potentially to levels of tension that were last experienced during the Cuban missiles crisis.
The other course of military action is aerial bombardment of Isis in Syria. David Cameron has made it clear that he would authorise military action against Isis in Syria, if he were able to secure Parliament's consent to do so. He has yet to offer any detail on the likely form of this action. The consensus seems to be that it would be based on the deployment of six UK fighter aircraft, despite widespread acknowledgement of the reality that Isis will not be beaten from the air and the absence of significant results after a year of combing by the US and others.
It is far from certain that the Prime Minister will ever actually get to the point where he feels able to seek the consent of Parliament when a sizeable chunk of his own MPs is opposed to his emerging plan, and he is currently struggling to assemble a cross-party coalition that would give him the numbers he needs. However, whether this issue ever comes to a vote is to some extent beside the point: the debate about the future of Syria is far too important to be confined by parliamentary arithmetic - it must be wider than Westminster.
In order to set the framework for the debate around the possibility of bombing Isis in Syria, we need to remind ourselves of some first principles, which are:
1. President Assad must bear responsibility for the vast majority of the 250,000 deaths and millions of displaced people that have been caused by this horrific war, and so it follows that the strategic aim must now be to secure peace and stability in Syria through the establishment of a post-Assad Government of National Unity (GNU) in Damascus.
2. The first step in that direction would be a conference of all the parties, but moderate Syrian opposition groups will only come to the table for peace talks on the basis of a guarantee that President Assad will step down, as part of the transition to a GNU.
3. In any transition there must be a clear separation of powers so that no one party or individual holds so much power as is the case now.
4. A roadmap to peace and stability is therefore required, starting with a conference of all the parties that would pave the way to the formation of a GNU. President Assad must commit to stepping down at some point along the timeline that is set out in the roadmap, as a pre-condition for the conference of all the parties to take place. However, he should be invited to participate in the initial meetings, as this will facilitate the transition.
5. The GNU would have to be based on a balanced and equitable combination of the moderate opposition and the current regime, with ministerial appointments approved by both sides. The formation of the GNU must be pragmatic, and based on learning from the catastrophic failure to undertake pragmatic de-Baathification in Iraq.
6. Any deal will require a ceasefire agreement and demobilisation. This will require a sizeable UN monitoring force, much larger than the 300 that was sent the first time around.
7. Aerial bombardment may serve to hinder the advance of Isis, but Isis can only ever be comprehensively defeated through a ground offensive by effective forces. Therefore it will only be possible to defeat Isis in Syria through a sustained military campaign that is led by the GNU and materially supported by an international coalition that should comprise the US, Iran, Saudi Arabia, Turkey, Russia, France and the UK.
8. Syria is a proxy war, with Iran and Russia supporting the Assad regime, and Saudi Arabia and Qatar backing the opposition. What all parties want above all else is stability, and in particular to avoid the contagious anarchy that would follow a forced regime change in Damascus. This pre-eminent desire for stability presents the only feasible opportunity for durable resolution. It offers the only possibility that Iran and Russia could potentially be prepared to abandon Assad in exchange for a stable Syria governed by a GNU. If the opportunity is to be exploited, both Mr Putin and the Iranian regime must now be engaged in the co-creation of the roadmap to peace and stability, and both must be offered firm incentives to do so.
With these basic principles in mind, it is possible to compose a political and diplomatic strategy that will achieve the desired objectives, starting with a radical re-think of engagement with Tehran and Moscow.
Turning first to Russia: my experience of living and working in that country for more than three years confirmed two fundamentals about Russia's attitude to the rest of the world; First, the Russians' top priority is to be treated with uvazheniye, with respect; second, their default position is to favour order and stability. Mr Putin's recent actions in Syria are a typically uncompromising reminder of these two deep-seated characteristics. He sees Syria as a Russian protectorate of immense geo-strategic value, and he will do everything in his power to ensure that Syria remains within Russia's sphere of influence. Moreover, he will not stand by as other regional and global actors "insult" him by trespassing on "his" territory without so much as a by-your-leave. It is impossible to over-estimate the importance of the role that national pride, uvazheniye and 'face' play in the shaping and execution of Russia's foreign policy.
However, there is no doubt that the Kremlin also recognises its limitations - and they are tightening. Militarily over-stretched by its campaign in eastern Ukraine and economically weakened by the dropping price of oil and by sanctions, the grandiose edifice of Russian foreign policy is built on decidedly shaky foundations. Interestingly, in a recent poll only 14% of Russians expressed support for military intervention in Syria. This weakness offers a real opportunity for leverage, and for some give-and-take that can lead to substantive diplomatic progress. The international community must now engage with Putin in a new way: conditional easing of sanctions over Ukraine in return for his full commitment to the roadmap to peace and stability in Syria. Of course there is a risk that such an approach could be framed as the west rewarding Russia for bad behaviour. We cannot allow this concern to shape our mind-set - the massive perils and costs of continued conflict in Syria and the region are too great for that, and we must also recognise that the moment we start to flex our military muscle then that 14% will rapidly become a far higher figure. We must now subdue convention and demonstrate that the prize of stability can be won, if all parties that want that outcome are prepared to compromise. As my colleague Jo Cox has so rightly pointed out, the plight of the Syrian people must now take precedence over all other considerations.
Looking then to Iran: the outstanding work of the P5+1 in delivering the nuclear deal with Iran has opened the door to a wider opportunity for bringing Iran in from the cold. The relationship between Iran and the international community is, for the first time in generations, characterised more by a spirit of compromise than of confrontation. The nuclear agreement was a much-needed reminder of the power of resolute, persistent diplomacy. We must now seize the chance to apply it to Syria. In return for their full and active commitment to the roadmap to peace and stability in Syria the Iranians must now be offered new channels of commercial and diplomatic engagement: the EU should offer trade talks, investment and development programmes should be designed, and platforms for people-to-people diplomacy should be fostered.
The reality is that neither of the two potential courses of military action currently being discussed will contribute to the strategic goal of delivering peace and stability in Syria: efforts to police an NBZ will almost certainly provoke a violent reaction from Russia and Iran, whilst air strikes against ISIS will only serve to bolster President Assad's position. Meanwhile, the moderate forces opposing Assad are being weakened further and the refugee crisis spreads and intensifies. Moreover, as Dr Neil Quilliam of Chatham House has stated, British military action against ISIS now would only serve to "reinforce the view currently held among Syrians that, despite significant humanitarian support, the UK government simply prioritizes the fight against ISIS over the lives of Syrians." Dr Quilliam also points out, correctly, that a decision to endorse military operations would strengthen the perception that the UK government is driven more by a desire for vengeance in the wake of the Tunisia atrocity than it is by a genuine desire to protect the Syrian people.
There can be no doubt that the Syrian crisis is spiralling out of control, and that US and EU attempts to develop anything that remotely resembles a coherent approach have been woefully inadequate. But it is not too late. Now is the time for our government to step into the vacuum; now is the time for our Prime Minister to show some leadership, and to start engaging in pro-active diplomacy in Moscow, Tehran, Washington, Ankara and Riyadh; now is the time for a roadmap to peace and stability. Clearly, we will have to compromise with Moscow and Tehran, and those compromises will certainly cause us discomfort along the way. But which is more important: losing face from the comfort of our green benches in Westminster, or striving to prevent the slaughter of thousands of innocent civilians, the endless misery of millions more, and the perpetuation of chaos in the Middle East?
The Syria crisis is a blood-soaked game of shadows. We must now learn and adapt to its rules; and we must start playing to win.