I'm really sorry but I am at work at the moment so I don't really have time for a proper cited argument, but in the mean time take a look at these:

http://tjm.org.uk/documents/briefings/post-brexit-report.pdf

https://capx.co/how-the-eu-starves-africa-into-submission/

The basic premise here is that the EU still treats much of the third world as nothing but a raw materials exporter and keeps a lot of the value chain inside of its own borders. This is especially true for goods like coffee, citrus fruits, soy, sugar, bananas and so on. I'll illustrate this with an example.

Let's say you're an enterprising coffee producer based in Ghana. Coffee prices are on the rise this year (as a result of some droughts in early 2017 in Brazil) and you have managed to save a decent cash pot for reinvestment in your company. You decide that instead of sending unroasted green beans to the EU, you would rather increase the value of your produce by building a simple roasting and packaging facility here in Ghana. This would allow you to add value to your product, create more jobs locally and develop your brand.

But while EU tariffs on unroasted coffee beans are 0%, this rises to a staggering 7.5% for packaged, roasted beans. Virtually the entire coffee industry opts to send their unroasted beans to facilities in Greece and Italy, and only there can they be roasted and packaged into final products. As a Ghanaian coffee producer, there's nothing you can do to get around this. You must resign yourself to the fact that you will always just be a producer of raw materials in the eyes of the EU, as opposed to a producer of high-quality value-added products.

You'll find that this is true for a wide range of different commodities. Read the labels of some of your favourite foreign foods and you'll see that many of them will say something along the lines of "grown in Kenya/Brazil/etc, packaged in Italy/Greece". The world is full of farming operations which are perfectly capable of conforming with EU standards and supplying foodstuffs into the EU, but they cannot because of the tariff escalation which occurs up the value chain. So they have to send in raw materials instead which have a terrible profit margin and do not support enough workers.

It's a terrible situation for everyone except for the coffee roasters in eastern/southern europe, and there's something awfully colonial about it all really. If we could relax tariffs on foreign goods once we have left the EU then that would mean that we could buy common goods like coffee much more cheaply, while also improving the lives of the citizens in the countries where they are grown.