THIS week the wheels really came off Theresa May’s Brexit proposals. Although, to be fair, that’s a statement you could have made at any point over the past months.

There is little to say about Brexit that hasn’t been said before – but it truly is an unprecedented, self-inflicted catastrophe.

So what should supporters of Scottish independence learn from the UK Government’s mistakes?

For a start, it’s deeply irresponsible to go to the people promising constitutional change without giving even the briefest thought on how to deliver it.

History will judge the likes of Johnson, Davis, Gove and Farage with contempt.

That’s one of the reasons the First Minister commissioned Andrew Wilson and a team of experts to re-examine our prospectus for the economic ambitions and structures of an independent Scotland, with their plans then scrutinised by SNP members through a series of National Assemblies.

Shaped by those discussions, my colleagues Derek Mackay and Keith Brown will lead a conference debate on our plans for currency, migration and economic growth.

When we ask people to vote for independence, we have a duty to put forward a serious and robust plan for how we’ll deliver it.

Reflecting on May’s failure and on the debates of 2014, one aspect of the Sustainable Growth Commission’s recommendations seems particularly astute.

There was never going to be a good Brexit. But the complete failure to deliver any sort of workable Brexit is entirely down to Theresa May’s mistakes. The Tories drew up self-defeating red lines – mainly to satisfy their own obsession with reducing immigration – and then seemed shocked that the EU would not bend to their will.

If you want negotiations to go well, it’s best to start them in good faith – while robustly defending your own interests.

Take the UK’s national debt. In 2014 the Treasury confirmed that all UK debt would remain the legal responsibility of the UK Government after Scottish independence. Scotland would start with no debt – not a penny, a cent, not a bawbie.

But we’d want to start negotiations on good terms to secure our fair share of UK-wide assets. It is in no country’s interests to start upon its journey towards independence at loggerheads with its closest neighbour.

Which is why the Growth Commission recommends that Scotland negotiates with the remainder of the UK to make an annual payment toward a reasonable share of the national debt for a limited period.

And let’s be clear on this recommendation, the commission is explicit in how we learn the lessons from Brexit. No good can come from negotiations where one side puts stubborn, imperious isolationism ahead of cooperating to secure the best outcome for all parties where that is achievable.

The think-tank Common Weal has unfortunately misrepresented this proposal in its attempt to influence the conference debate. That’s something that, as someone with respect for their work, deeply disappoints me.

They have claimed that we would accept debts without negotiation and make an annual payment “forever”. That’s not the case, it’s not what the commission says and it’s not what is being proposed to conference.

The Growth Commission report is clear – it says that “we would expect the true value of assets and liabilities to be examined and debated with greater rigour in advance of agreement being reached”. In other words, we will negotiate, and negotiate hard from the start, but by entering that process in good faith we can expect a better outcome.

Secondly, the commission sets out very clearly that any annual payment would diminish year on year in real terms – and any attempt to claim otherwise is deliberate and disappointing misrepresentation.

The demonstrative model that the commission uses to explain how a solidarity payment could work in practice, sets out how it would become negligible over time as we grow our economy through independence.

And it’s important to remember that 30 of the 50 recommendations set out by the Sustainable Growth Commission concern how Scotland’s economy could grow to at least match the best small economies anywhere in the world.

That payment could also include payment for any services or international programmes that Scotland wishes to continue to share or to co-operate in. The key word here is “could” – if a democratically elected Scottish Government chose to do so, they could share services for a short, or an extended, period. Or they could choose not to.

Scotland already works with other organisations and countries when it is appropriate to do so, at home and abroad. It is ridiculous to suggest that uniquely amongst nations we would not work with the rest of the UK. The difference is that we would finally be doing so as a sovereign nation making our own decisions in our own Parliament.

Let there be no doubt, as and when Scotland votes for independence, we will not repeat the errors of Brexit. We will negotiate as equals and we will take a sensible, hard-headed approach to becoming independent.

And if the motion that Keith Brown and Derek Mackay have put to conference is passed we will be able to use those negotiations to lock in solid public finances, a strong economy, and the basis on which to expand and build newly independent public services. Our proposals are fair to both Scotland and the rest of the UK and crucially do not repeat the mistakes we are seeing being made by the UK Government.