Change Britain – the “campaign to make a success of Britain’s departure from the EU” – published a “report” on the economics of Brexit yesterday. I described it as “junk”. But one response to my comments was interesting – and surprising: Michael Gove tweeted that “hard cheese and sour grapes are never a good combination”.

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It wasn’t clear who this was directed at, but I thought I’d respond. After all, Gove is a “founding supporter” of Change Britain. Surely someone of his undoubted intelligence would have a reasoned view about the claims it made? So I asked him if he endorsed the report. He first responded with some general, and irrelevant, rhetoric. Then I asked him if he’d even read it. Here’s what happened next:

Apparently Gove thinks his earlier comments on “experts” have been misinterpreted. He said today: “I think the right response in a democracy to assertions made by experts is to say ‘show us the evidence, show us the facts’.”

Fair enough. But his response to me wasn’t to talk about evidence or facts. It was to refuse to engage in discussing facts – or to defend the false claims made by his campaign – until I said, publicly, which way I had voted. And to imply that the expert opinion of anyone who isn’t prepared to come out and say publicly that they didn’t vote remain is, by definition, biased.

Of course, the most charitable explanation of this bizarre exchange is that Gove was attempting to deflect attention away from the Change Britain report itself. When I said it was junk, I was being a bit kind. As Sam Bowman explains, the report arrives at its conclusion that Brexit would “boost the UK by £450m a week” by adding together potential savings to the Treasury from eliminating our net contribution to the EU budget, to the (hypothetical) increases in exports from post-Brexit trade deals, to the supposed benefits of eliminating some EU regulations (mostly the Data Protection Act).

This is worse than adding apples and oranges – more like Christmas pudding, brussels sprouts and a pint of sherry. Indeed, the direct impact of trade deals – while they may boost the economy – is actually going to cost the government money (as tariffs are reduced or eliminated), not save money.

Whatever you think about the economics of Brexit, the Change Britain report is laughably incompetent

This was far from the only error: the report also claims as a potential gain from Brexit increased exports from a free-trade deal with South Korea. The problem is that the EU already has a free-trade deal with South Korea – in force since 2011. Would this continue post-Brexit? Probable, but not certain. In other words, not only is free trade with South Korea not a potential economic benefit from Brexit, it’s a potential cost. Whatever you think about the economics of Brexit, this is laughably incompetent.

More broadly, this tells us something about the state of the current debate on Brexit. We mock Donald Trump’s clumsy and obvious untruths. But when Change Britain produce a report that contains equally patent nonsense, badged as “research”, some newspapers are happy to report it uncritically. And senior politicians like Gove are equally happy to promote it – and when challenged, resort to ad hominem attacks on the supposed motives of “experts” who are simply trying to do their job.

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This does not bode well for those of us, inside and outside government, who are trying to produce detailed evidence and analysis to inform the public debate. Over the next few months, the UK will face a set of choices that will shape our economic destiny for decades to come. What are the trade-offs between attempting to, as far as possible, replicate the current arrangements for trade between the UK and the rest of the EU and regaining the flexibility to shape our own arrangements with the rest of the world? Should we seek some form of transitional arrangements to avoid the potential disruption of an early and abrupt exit – and if so, how to avoid the risk that we end up in a semi-permanent limbo? And so on?

If we’re going to have a constructive, sensible debate on these issues, we need proper analysis, by real experts, not propaganda; with, as Gove says, evidence and facts. Not – as Anand Menon and I suggested before the referendum – to tell people what to think or to try to convince them that they voted the right or wrong way; but so that there is a common, evidence-based framework for discussion.

For example, in the new year my colleagues and I from The UK in a Changing Europe intend to publish a short reflection – some “tests”, if you like – on what a “Brexit that works for Britain” would (and would not) look like. Would it make the UK a more open economy and society or a more closed one? Would it make the UK fairer – especially for those who haven’t shared the gains of the last 20 years – or less so?

We’ll put forward a rigorous – and objective – attempt to provide a framework for answering these questions. If Gove – and others on both sides of the argument who seem more interested in refighting the referendum – actually want to play a constructive role in what comes next, then maybe they will engage properly with this and other forms of expertise, rather than insisting on some sort of loyalty test.