These days, I never travel without my Brexitometer. It measures two things: the time elapsing from the opening of any conversation to the first mention of Brexit (average: three minutes) and the proportion of all those I encounter who think Brexit is a good idea. Over the past two months, I’ve been in America, Canada, Germany, Austria and Poland and the second metric is currently running at about 1%. The other 99% think we Brits have gone stark staring bonkers. How could people known throughout the world for their pragmatism, empiricism and common sense do something so obviously contrary to their own interests? The emotional timbre of this questioning is not anger or despair but rather a kind of melancholy incredulity.

Now of course Brexiteers will jeer that my 99:1 ratio only reflects the kind of irredeemable Europhiles I consort with, but actually I have sought out the widest possible range of people. Adjust the ratio if you will – 90:10, even 80:20 – but anyone who imagines that most of the world thinks Britain has done something smart is living on another planet. The fact that it may be Planet Trump is small consolation.

The starting point of any “what’s to be done about Brexit” analysis is thus a deeply depressing one. By a narrow margin of 52% to 48%, Britain has decided to inflict lasting harm on itself, on Europe and on the wider framework of liberal international order. The best we can hope for in the foreseeable future is to reduce that probable harm as far as possible, and polish such small silver linings as may be discovered inside a giant rain cloud. In essence, the next five to 10 years of British politics will be a quest for the least worst.

German chancellor Angela Merkel: European elections, especially the French and German ones, ‘will affect the position taken by our European partners when push comes to shove at the negotiating table in 2018’. Photograph: Tobias Schwarz/AFP/Getty Images

How to set about that dreary task? So much is uncertain that it is foolish to commit to an over-detailed game plan. I think it’s a mistake for the Liberal Democrats to campaign now for a firm commitment to a referendum on the negotiation result two years hence. And it’s doubly mistaken for the party leader Tim Farron to make this a party-political pitch for the Lib Dems against Labour, as he does in the latest issue of the New European.

Rather, we need a combination of strategic firmness and tactical flexibility.

At this stage, what’s essential is to make sure that triggering the article 50 exit negotiation is subject to a parliamentary vote, and that an interim result of the negotiation is brought back to the floor of the house in, say, autumn 2018, giving parliament sufficient time to consider and shape it before the two-year deadline is reached. Parliament must be sovereign in restoring parliamentary sovereignty.

It is becoming clear that there will probably be three steps to be negotiated: the terms of exit, which is what article 50 provides for; a transitional agreement, since nothing as complex as an entire new relationship with the EU has ever been negotiated within two years; and then the final deal. In giving the mandate for what is probably a three-step negotiation, parliament should insist that the options of full access to the single market and, alternatively, being in a customs union, are comprehensively explored with our European partners.

Recent polling by NatCen Social Research, reported in the Economist, shows that most of those asked, on both the leave and the remain sides, want to “allow the EU to sell goods and services freely in Britain and vice versa” but also to “treat people from the EU who want to come to live here like people from outside the EU”. So they consciously or unconsciously subscribe to the Boris Johnson doctrine – have your cake and eat it. Confronted with the outrageous possibility that Britain might not be able to have its cake and eat it, and specifically with the trade-off “allow freedom of movement in return for free trade”, a clear divide opens up between leavers who say no to that and remainers who say yes.

So central is this issue that we must know concretely what would be on offer, and the only way to find that out is by putting it on the negotiating table. We should not, however, insist on the government committing itself publicly to a detailed negotiating plan. The letter to Brussels opening the article 50 negotiation should be as short and open as possible. This will also make it easier for the other 27 member states to agree a short and open response, and hence get the talks under way.

Forget the Brexiteers who say 'they need us more than we need them'. The continental 'them' see it differently

There is something unreal in the current British debate about “whether to go for soft Brexit or hard Brexit”. At the end of the day, whether we have a hard or soft Brexit will depend more on others than on us. Let’s be absolutely clear: a negotiating position where you have a specified two years to reach a deal (even if the clock can be stopped for a time) and you need 27 other states to agree to it (even if the last leg is theoretically by qualified majority voting) is a very weak one for Britain. And the stock of continental goodwill has been depleted by decades of Britain being an awkward partner. Forget the flaccid Oxford Union-style braggadocio of the Brexiteers who declare “they need us more than we need them”. If you talk to them, the continental them, they somehow see it differently.

Over the next 12 months we have an Austrian presidential election, a referendum in Italy, a Dutch parliamentary election, a French presidential election and a German general election. All of these, and especially the French and German ones, will affect the position taken by our European partners when push comes to shove at the negotiating table in 2018. Moreover, we don’t know how palpable the negative economic consequences for Britain of the uncertainty around Brexit will have become by then.

Forecasts by the independent Office for Budget Responsibility and the Bank of England are more professedly uncertain than those before the Brexit vote – and anyway, these are just numbers. The real question is how far British voters will already feel the economic pain, and fear it getting worse, at the crunch point when Britain has to decide what deal to go for.

In a period like this, with so many known unknowns, wisdom lies in agreeing a rigorous parliamentary process, informing the public of the real facts and hard choices, careful diplomatic preparation, keeping options open – and watchful waiting for a moment of opportunity. This may sound dull, but who said Brexit would be fun?