David Hannay is a member of the House of Lords and former UK ambassador to the EU and UN.

If anyone seriously doubted the marginalisation of British diplomacy, then surely its absence from this weekend’s meeting between the leaders of Russia, France, Germany and Turkey to discuss the future of Syria will have stilled any such doubts. Neither as an EU member with its hand on the exit door nor as the standard bearer of a “Global Britain” due to emerge onto the world stage next March, was the UK considered worth inviting to that conclave in Istanbul.

The inability of the government to chart any sort of foreign policy course as it struggles through the Brexit quagmire merely accentuates that marginalisation. Some months ago three former heads of the UK’s diplomatic service, together with the present writer, urged the then (and not greatly lamented) foreign secretary, Boris Johnson, to appoint a full time special representative for Syria so that the UK could play some role in shaping the future of that country as its civil war showed signs of petering out. Not a hope. The foreign secretary was too busy on other matters to entertain such an idea.

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If the Syrian example is not enough, how about the revelation that our closest ally, the United States, did not bother even to consult the UK before announcing their intention of withdrawing from the Intermediate-Range Nuclear Forces Treaty with Russia, which restricts the use of nuclear missiles? And that despite the fact that the UK, alone among America’s main European allies, is reaching Nato’s defence spending target of 2% GNP – and has been urging the laggards to catch up.

Both these developments are portents of what life after Brexit will be like for Britain’s diplomacy. The Brexiters are always urging us to be more cheerful about that prospect and to appreciate the great opportunities awaiting us there. All the evidence is that they do not exist, and that we will no longer be regarded as a privileged interlocutor by either Washington or Brussels. That is surely a long way from what people voted for in June 2016?

Edited by Luke Lythgoe