Presuming that we accept the will of the British people and leave the EU, my own position is that we should move to either a transitional arrangement that keeps us in the Single Market, or adopt a permanent position that includes Single Market membership. I think this is possibly where the UK will end up, wilful Brexiteers nonwithstanding. I accept the evidence that says the overwhelming majority of the British public do not want to cut immigration if it costs them personally a single penny, and venture that we cannot read more into "a simple In/Out referendum" and it is revisionist to try.
So, starting from that point here goes.
However, what we need to do is look to the positives of this, not necessarily "Project Fear" or spending the whole argument on the back foot, rebutting whatever nonsense is being produced by the Hard Brexit camp. We need to make a positive case.
The three reasons I will put forward to stay within the Single Market are built around concentric circles - the status of the individual, the status of the UK and the status of the World.
1. Citizen's rights
Plenty of UK nationals live abroad in the EU - 1.2 million is a good estimate . Their rights have been regarded as a bargaining chip but the right of residence by it's very nature should be inalienable. Removing rights from citizens is a serious business, not to speak of the fact if there is a deadline for removing rights from people, you'll find many unintended effects such as those who are able to, start moving to places where their right will not be removed.
We also have the right of freedom of movement around the EU. My proposition of remaining within the UK is a positive for all UK citizens, meaning they can continue to enjoy their rights of living and working within the EU. This is also a positive for businesses wanting to hire from other countries.
3. Economic direction of travel.
Joining or staying in the Single Market has been our strategy for the last 40 years. There is potentially a case for moving to being a different sort of economy, however it's a borderline impossibility to, as it were, turn the tanker [of the British Economy] around on an Article 50 shaped sixpence.
Our current account deficit is relatively very bad next to other OECD countries.
We import far more goods than we export, tho we do have a surplus in services (i.e. we export more services than we import). It is important that our economy becomes more balanced and I do see this as an important policy objective, but we cannot do it overnight. Therefore, to offer certainty to businesses, we need to have a model with minimum disruption, at the very least in the short term.
It appears the British public agree
It is also imperative given the current account deficit to at least preserve the surplus in services, so we must make sure that people continue to be able to work in the EU where they are needed, with as little friction as possible.
2. Globalisation and it's contents
The fact that took us into the Single Market, known as the Common Market in 1975 was the part of a wider move by the world towards globalisation, and it was important that we did this, so as not to be left behind. The Labour government, and later the Tories (at least the leadership whilst they were in power) did understand this intuitively. Remaining close to our main trading partners is not merely desirable, it's imperative.
The world senses that removing trade barriers and encouraging migration is a good thing, and the more it happens, the less poverty and war there will be. Though contentious, this "less war" theory is advanced enough an idea to have a name and that is Commercial Peace
Morally, to be honest, all global citizens should be thinking about being drawbridge down type of people, as it leads to less poverty, less war and more value being created worldwide. Citizens of the UK and the World, this could indeed us taking part the Great Global Move Forward, if we are brave enough to do it.
I put it to you that with these three points in favour of remaining in the Single Market, that this is what the UK can and should do.