Outsideinthegarden is no economist.
For a start, he derided someone for saying that investment was leaving the country using a statistic which showed inward FDI in the first quarter of 2018 ( note not net FDI or FDI credits which would be the true metric of this) he then went on to make a claim that it showed that the UK was a far more attractive place to invest based on the nominal value of this inward FDI flow. However this is incorrect, the value of the Dutch FDI is more than double the UK's as a % of GDP and the Spanish is the same. Per capita the Dutch is also more than double that of the UK.
I'll elaborate further, FDI is also not a good measure of investment because it can include acquisitions of domestic firms by foreign companies, this has increased in the UK with the fall in the £. However using FDI this means that using measure of the viability of a copuntry isn't great, 70% of the UK's net FDI in 2016 was two deals. £79bn take over of London SABMiller ( mainly US operations) by Anheausser- Busch and the take over of a UK chip maker by a Japanese firm. Neither of these resulted in any capital of human capital investment in the UK.
The ONS actually showed that investment fell ( from both national and international firms by 0.7% in the three months to the end of June.
However if you were an economist you'd know that right?
To sum up, using nominal values rather than contextual, whilst making claims about figures that don't stand up to scrutiny is either wilfully disingenuous or suggests that they don't know what they are talking about.
Furthermore they didn't understand about MFN status in EU trade deals, they made a comment about the "extra cost of transporting cars" to the continent, without realizing the technical economies of scale brought by containerisation.
Additionally their claim that the EU is protectionist is deluded, the EU offers the most open market to its members, and protects this from non members, like all trade blocs. The idea that outside the EU is non protectionist is ridculous. The discussion of rolling over trade agreements also shows a vast misunderstanding of international trade as does the point regarding 90% of the economic growth being out of the EU ( doesn't mean we will have anything to trade with these growing countries does it, nor does it mean that being in the EU prevents trade)
Furthermore no real economic argument has been made about brexit, just fallacious attacks littered with appeals to emotion and history. Demonstrating a vast lack of critical thinking.
I could go on, but all in all, if outsideinthegarden studied economics, they did so at the early learning centre.