Re: Brexit means brexit.
"Sovereign nations do trade: they trade as sovereign nations ... You would fail GSCE politics" --- Dr Stephen Jones
When he says "No countries are sovereign" he clearly means in the (incorrect) sense frequently used by the Brexiteers desperate to "reclaim it" --- they seemed very often to use it to mean total independence from, if not absolute domination of, all other nations. Many of them ironically also seemed to think that the idea that T. May could not decide the terms of Brexit all on her own without reference to Parliament was also an affront to UK Parliamentary sovereignty when it was in fact the very opposite.
Obviously we all know that nations are sovereign in the proper sense of the word. But, unlike the vast majority of Brexiteers, we understand that treaties etc are, in a sense, a trade off of some sovereign power for some other advantage. Naturally we never lose the sovereign power itself, but we agree to be bound by certain conditions in exercising it. Because we actually never yield sovereignty, we can rip up those agreements if we choose (e.g. by invoking Article 50). But in the sense the word was mis-used by many Brexiteers ("we want our sovereignty back") he is absolutely correct that there are no sovereign nations.