As I said at the end of my last blog on Brexit and the energy sector, the whole debate on Brexit right now is based on speculation.

No-one has much of a clue what the UK’s post-Brexit relationship with the EU might look like, nor in truth do we really know whether the new settlement hard fought for by David Cameron will actually improve things for the better.

At least in an election, a voter can weigh up the relative strengths of the rival party policies, and can look a politician in the eye and assess whether he or she is trustworthy.

But with the Brexit referendum, do we really know what we’ll be voting for?

A vote to remain is perhaps an endorsement of sorts of the status quo, with a leap of faith thrown in that the PM’s deal might indeed make things better. And it will mean, for some, a casting to one side of any cynical belief that this might all just be a reckless high-stakes game of poker designed to sort out the schisms in the Tory party once and for all.

A vote to leave, however, is more difficult to pin down, beyond a statement of dissatisfaction with the status quo or a gut feeling that the new deal with Europe will just make no difference. What vision for the future are we being sold?

Hence the so-called “Project Fear” and much talk of lurching into the unknown.

Which is why it was at least encouraging to hear Boris Johnson make some attempt last week to paint a picture of what a post-Brexit UK-EU relationship could look like.

And in pinning his hopes to a Canada-type free trade deal, the London mayor is at least putting to rest any suggestion that Norway or Switzerland might offer a blueprint for the UK.

Now I’m no constitutional expert, but it’s worth taking a look at some hard facts on Brexit options.

First, unless the UK wants to effectively declare UDI Rhodesia-style, there is only one legal route to the exit, and that’s in Article 50 of the EU Treaty. If we ignore that, we’re in breach of international law.

Under Article 50, after a leave vote, the UK would write a formal letter to the EU invoking the process. That would kick off a 2 year period for a deal to be negotiated, after which all EU treaties stop applying to the UK and we’re out on our own.

Whilst Summer 2018 might seem a long way off, remember this will be a negotiation not just on the tricky exit terms but crucially on what that future relationship is going to look like.

Any successful negotiation needs willing and constructive parties on all sides, and we should reflect that a straightforward and seemingly benign (for the UK) negotiation process is unlikely to be overly helpful in political terms for our EU partners. And throw in some critical elections in France and Germany in 2017, not to mention some likely political ructions here in the UK if the vote is to leave, and these negotiations look set to be fraught.

Assuming a deal can be reached in time, it will on the face of it need approval of 20 of the remaining 27 member states, plus majority approval of the European Parliament. But that’s only if the deal doesn’t stray beyond mere exit terms, because in many other areas unanimity could be needed.

And if negotiations get bogged down and we approach the end of the 2-year period with nothing to show, then Article 50 says that any extension needs all 27 other member states to unanimously agree.

So, it’s not hard to foresee the prospect of individual vetos and horse-trading right down to the wire. The Article 50 process was not designed to be easy.

But all this is process – what are the options on the table?

A Norway deal could be a “quickie”. It would involve rejoining the European Free Trade Area (EFTA) - which we left back in 1973 in order to join the predecessor of the EU - and becoming a party to the European Economic Area Agreement (EEA) Agreement so as to give us full access to the single market.

But signing that agreement involves compliance with large swathes of EU law in areas like employment, consumer protection, environmental policy and company law, as well as adherence to the four “freedoms” – of goods, services, people and capital.

Whilst the EEA Agreement notably does not cover agriculture and fisheries, justice and home affairs and foreign and security policy, the EFET option does look and feel like leaving the EU but re-signing up to most of the stuff from the outside.

And two key points here. First, we would lose a seat at the top law-making table; EFET countries are policy “takers” not “makers”, which might be OK for the likes of Norway, Iceland and Liechtenstein but surely not for the UK. Second, EFET states all pay contributions to EU coffers to access the single market.

A second option is a Swiss deal; Switzerland is also an EFET member, but instead of signing up to the EEA Agreement has been able to negotiate around 120 separate bilateral deals with the EU to allow it access to the single market. But this is a complex state of affairs, it’s unwieldy, and is probably not on the table.

So instead of the EFET route, the best option is likely to be leaving the single market completely, and negotiating our own comprehensive free trade agreement – as Boris says, like Canada.

Without such a deal, we would certainly have access to the EU market, as they would ours, through membership of the World Trade Organisation, but a trading relationship based on the WTO would come with the full panoply of tariffs and trading restrictions.

One thing to bear in mind about trade deals is that they don’t happen quickly. Talks with Canada have been going on since 2009, and the ongoing talks between the EU and the US have some way to go still.

And before we get too carried away with Canada as the latest blueprint deal on offer, we should remember that a deal such as that would do little to protect the City and its global status – one of the battlegrounds of the whole EU in/out debate.

The challenge for the Leave campaign, coming as it does from what would be only one side of the negotiating table, is how it can present these possible options (short of co-opting Mystic Meg into the campaign) as anything more than speculation and best-guessing.

Certainly, between now and referendum day, the EU has absolutely nothing to gain by making that job any easier.

That’s not to say the Remain campaign doesn’t have its own challenges. When it comes to a politician looking us in the eye and earning our trust, how can we do that in the case of an institution made up and representative of 28 diverse countries? Especially so when the head of the otherwise largely faceless but all-powerful EU Commission is an individual whose trajectory to the top David Cameron did his very best to de-rail as a man the UK could not do business with.

This referendum is about a vote for the future but not the sort we’re used to, and the campaign days that lie ahead are not going to be easy ones for the protagonists on either side of the debate.

* Andrew Whitehead is senior partner at law firm Shakespeare Martineau and leads the firm’s energy and climate change practice.