Next May would be the best time for the EU referendum, but speed is essential in launching the Yes campaign

Like nature, financial markets and international investors abhor a vacuum. After the Conservatives’ modest victory on 7 May, there is now a huge vacuum where there used to be the assumption that Britain was a member of the EU: no small matter. That unstable situation will remain, and continue to do damage, for as long as it takes to complete the long-awaited “in-out” referendum.

The optimal time for it would be next May, coinciding with elections in Scotland, Wales, Northern Ireland, London and some local authorities. The level of interest and coverage could ensure a higher turnout for all these polls, and, in the case of the referendum, a more convincing verdict. The higher the turnout and the greater the margin of victory for staying in the EU the better, so far as settling the issue is concerned. One useful bonus from a quick Yes vote would be that Ukip would cease to have much relevance.

An earlier referendum would also avoid the traditional problem with such plebiscites, namely that they get caught up with the general discontent with an incumbent government during the usual midterm blues. As some of our partners – France, the Netherlands and Ireland, notably – have found, referenda can quite rapidly go wrong under an unpopular government. An accidental No vote would be the worst of all possible worlds.

Business and the Bank of England – who understand the economic implications of a Brexit better than most – are on the side of staying in, in practice, regardless of whatever marginal concessions David Cameron is able to extract. Although the EU’s institutions are notoriously slow, it would be in the best interests of Europe as a whole for them to end the renegotiation charade as soon as possible. The Prime Minister should be allowed some face-saving changes, especially on paying benefits to EU migrants – and much of the preparatory work for the “historic breakthrough”, as it will be spun, has already taken place.

All of which makes more urgent the launch of the pro-Europe campaign. To avoid it being unduly partisan, it might be best if, as in the 1975 referendum campaign, the sole precedent, it was not headed by a current party leader, though they should certainly be involved. A former leader might be a good choice. In any case, the Yes to Europe grouping will contain all the political and business figures the public know well and, to the extent they trust anyone in public life, are prepared to listen to.

By contrast, the No campaign will be dominated by Nigel Farage, Bill Cash, Arthur Scargill and maybe some Tory leadership rival willing to take a gamble, such as Liam Fox, say: not a telegenic face between them. The danger, in fact, is that the Yes campaign looks rather too cosy and “Establishment” for some, while the No campaign poses as popular insurgency.

Finally, the Government needs to be clear about whether, if the UK as a whole votes to leave but Scotland wants to stay in, then Scotland should be allowed an effective veto on the decision – as should Wales, Northern Ireland and England for that matter. Leaving Europe is not something that should be done against the wishes of the British people, and nor should it be done against the wishes of any of the four constituent parts of the UK. Mr Cameron could both demonstrate his respect for the wishes of those four nations, and further his own baser political purposes, if he were to do so. But he does need to get a move on.