It is a measure of the desperation sensed by those trying to end the civil war in Syria and stall the onward march of Islamic State that a proposal for a UN mandate for the country has not been dismissed out of hand. The suggestion was aired this weekend by Gilbert Greenall, a veteran international relief adviser, who mooted the creation of a structure similar to the one set up by the League of Nations that administered Syria between 1923 and 1945.

While the idea seemed to come almost out of nowhere, there were hints that talk of a mandate had quasi-official roots. Reports mentioned support in Whitehall for an accelerated UN role.

The UK has – to put it mildly – a contested history in the region, and is now also involved militarily. So the intention could be for others – possibly the US and the Russians together – to pick up the proposal and run with it.

And the initial UK response, at least, seems more positive than negative. Paddy Ashdown, one of the few people with experience as something akin to a post-colonial overlord (as high representative in Bosnia) said it was worth considering. So did the Labour MP and ex-serviceman Dan Jarvis, who saw the formation of the Afghan army and police as a possible precedent. The former foreign secretary Malcolm Rifkind was also open to such an arrangement, while warning that a political consensus would need to come first. Any armed presence would have to come principally from the region, to avoid any impression of a new “crusade”.

But why, if it has so much going for it, is the mandate idea being canvassed only now? One reason is the absence of anything else that might preserve Syria as a state and fend off the threat of a regional conflagration from Lebanon and Jordan to Yemen and Iraq.

Another would be the changed balance of forces since Russia – and to a lesser extent, Britain – became involved. A hallmark of Soviet, and now Russian, foreign policy is a preference for international structures. The UN is already involved in the talks that began in Vienna at Russia’s instigation (and which continue in Riyadh this week), and four of the five permanent members of the UN security council are now engaged in air strikes on Syria. A greater role for the UN would be a logical progression.

The flaws, though, are obvious. The first is that the conflict in Syria began as a civil war. If the parties to the civil war are not ready to contemplate its end, even in order to stop the predations of Isis, it is doubtful that outsiders – however big, powerful and consensual – will be able to enforce a settlement for long. Then there are the proxy conflicts also being played out in Syria, with Saudi Arabia, Turkey, Iran and now Russia all pursuing interests of their own. No one, it seems, is ready to blink.

Yet the very complexity of the Syrian conflict makes the UN probably the only body able to set a framework for a settlement and then stand as its guarantor. Which brings us to the vexed question of the “day after”. Could, and even should, the UN go the whole hog and assume a mandate for Syria? Is this perhaps why things went wrong in Iraq and Libya?

The idea has to be tempting – as tempting, no doubt, as it was the first time around, following the collapse of the Ottoman empire. And there are those who argue not only that colonialism has been judged unfairly, but that a new colonialism would be the best remedy for bad governance anywhere in the world.

Would a UN mandate be feasible, however, in the connected modern world, where the cry is more often for self-determination? Perhaps it would. On the Maidan in Kiev, the calls were for closer relations with the EU, but they were primarily a plea to Brussels to come and sort the place out – and in some ways, it is now a voluntary colony of the EU. Something similar could be said of Bosnia and Kosovo.

But could there be enough of a national consensus in Syria to accept a UN mandate for the sake of keeping the country whole? Would security be sufficient to prevent neighbours (and others) nibbling bits away? Could there ever be agreement on a governor? Would those who underwrite the UN be prepared to pay more for it to do more?

Even if all the answers were yes, the most awkward question would remain. Why devise a new mandate for a part of the Middle East, when business from the last mandates remains unfinished. Three generations of stateless Palestinians should remind us that botching the job last time around helped create the mess Syria faces today.