Five years ago, dozens of journalists made their way to Bloomberg HQ in the City of London to hear the then prime minister David Cameron make a speech. I was among them.

This pledged a future Conservative government to put renegotiated membership of the European Union to a referendum. At the time, this seemed rather academic, for Cameron didn’t have an overall majority, something that seemed unlikely to change following the 2015 general election.

Of course, that’s not how things panned out. The Tories’ unexpected majority in 2015 – rather like Alex Salmond’s in 2011 – escalated the referendum timescale. Cameron called it early in the belief it would be easier to win. He gambled on that point and failed. The then first minister delayed his plebiscite with the same goal in mind. He also failed, but for different reasons.

Video: SNP accused of Trump-like attack on critic in broadcast

For what it’s worth, I’ve never bought the idea David Cameron could have avoided holding a referendum any more than he could have resisted the SNP’s calls for an independence ballot after 2011. Indeed, at Bloomberg that morning in January 2013, Cameron linked the two referendums under questioning, making the reasonable observation that both issues needed resolved one way or another.

Where Cameron erred was in the complacent assumption he could somehow overturn several decades of Eurosceptic drizzle within the space of a few months. In his 2005 campaign to become Tory leader he won over Eurosceptics with his pledge to withdraw Conservative MEPs from the European Parliament’s centre-right bloc. That might have seemed a minor concession at the time, but it proved a slippery slope.

All of this now looks like ancient history, whereas 2018 will be the year in which the rubber – as the Americans like to say – meets the road. Last week also demonstrates how bumpy that road will be, with the Scottish Government publishing its updated paper on “Scotland’s Place in Europe” reiterating a “hierarchy of preferred outcomes”, ie continued EU membership for Scotland and, failing that, the whole UK remaining within the single market and customs union (SM and CU).

This remains a reasonable position, just not one that seems likely to be realised. Fundamentally, neither the Conservatives nor Labour are prepared to compromise on freedom of movement, and without that continued membership of the SM and CU is impossible. Attempting to square that circle naturally produces linguistic contortions, such as that of the shadow chancellor yesterday morning.

Video: SNP accused of Trump-like attack on critic in broadcast

Outlining Labour’s position, John McDonnell said it “would not be the same single market” but “access to a single market”. That, of course, is a meaningless distinction given the clear position of the EU itself. Compared with that, the SNP’s stance is a model of clarity and consistency; only when one examines the Scottish Government’s third “preferred outcome” does the position become less clear, for it still hasn’t convincingly explained how Scotland could maintain membership of the SM and CU if the rest of the UK leaves.

For the time being, however, all eyes are on the next stage of UK-EU negotiations and, in Scotland, talks between Edinburgh and London to avoid a constitutional “crisis” this Easter. This road has also proved rocky. Until late last year it looked to be on track, before the Irish border issue briefly caused a pile up, while last week the UK Government didn’t table, as promised, amendments to Clause 11 of the EU Withdrawal Bill.

This obviously wasn’t ideal, although a number of events – including Damian Green’s resignation and a delay to the Bill’s Report Stage – made it impossible. Both governments, however, remain confident of reaching agreement on what is a purely technical (but also politically symbolic) process.

In a speech to the David Hume Institute (DHI) last week, Nicola Sturgeon spoke of the bill (as it stands) running “completely counter to the basic principles of devolution”. Now although the 1998 Scotland Act envisaged no such scenario, the First Minister has a point. Basically, the UK Government has to find a way of altering Clause 11 so the Scottish Government is satisfied those “basic principles” are not undermined.

This is difficult, though not impossible. Edinburgh, importantly, accepts the need for “common” UK frameworks in certain areas but, in essence, wants first dibs on all the powers presently shared with the EU before handing any back to London, for example when it comes to agriculture. Assuming there’s agreement, a Legislative Consent Motion will pass at Holyrood and peers like the lords Hope and Wallace (of Tankerness) will then ensure it gets through the House of Lords.

Both the Scottish and UK governments, meanwhile, are conscious all of this is, as one close to the process puts it, “an anorak issue with no connection to real people”. In other words, deriving political capital from it – even were negotiations to come unstuck – would be incredibly difficult. Both, therefore, are playing a waiting game: Conservatives believe most Scots accept Brexit will take place, while the SNP hope that once everything has “shaken out”, public opinion will move in their favour.

Time, however, might not be on the SNP’s side. In her DHI speech, the First Minister also spoke of 2018 as a “crucial” year, one in which “rhetoric finally meets reality”. She meant, one assumes, the rhetoric of the more optimistic Brexiters, which was fair enough, but equally it applies to Ms Sturgeon, for by the autumn she will have to show her hand – once again – in terms of her own constitutional ambitions.

Video: SNP accused of Trump-like attack on critic in broadcast

A fascinating recent YouGov poll showed that Remain voters are more anti-independence than pro-. Continuing to pitch to the Yes-Remain camp, therefore, looks increasingly like a dead end, particularly as Yes-Leavers presumably won’t like what they’re hearing from the SNP. Brexit, in other words, continues to be subject to the law of unintended consequences.