A thread on an issue arising from this piece: VAT/excise and the difference between internal EU borders and an EU/third country border (eg the Channel and @BorderIrish after Brexit).
I earlier pointed out the differences from a VAT point of view between the EU external border and EU internal borders: those differences are important in evaluating claims that because there is no need for infrastructure at @BorderIrish now, there wouldn’t be post-Brexit.
That makes the point that current arrangements on VAT and excise between Member States rely on cooperation and harmonisation. Extensive cooperation on information about import flows and harmonisation of basic approach, exemptions, and rates (within ranges).
It’s worth thinking a bit more about harmonisation. EU legislation permits VAT and excise (fuel/tobacco/alcohol) rates to diverge. But within bounds, set out in agreed Directives.
If the U.K. is no longer bound by those Directives it could do anything. Outright abolition is unlikely. But setting up a VAT- and duty-free port in Dover or Fermanagh? Or removing VAT on particular high value or transportable items.
Either would create a serious risk of leakage from EU VAT receipts, by EU consumers or smugglers. That risk of leakage goes beyond what is currently regarded as tolerable within the EU: and would require border checks.
And remember that current trade patterns across borders can change markedly where there are possibilities of making or saving money from arbitrage.
So it’s hard to see how excise and VAT checks are avoidable if the U.K. insists on freedom to diverge on VAT and excise beyond the divergence currently permitted to Member States under the relevant directives.
But the Chequers White Paper wants to avoid any new declarations or border checks for VAT and excise purposes. (NB this is about Dover-Calais, not just Fermanagh-Sligo.) 
It concedes “common cross-border processes and procedures”. But for the reasons given above, I can’t see that that will be enough.
It seems to me that - for the reasons set out - to avoid VAT and Excise checks at the border the U.K. will have to stay in the VAT and Excise system more generally: structure, exemptions, rates, and supervision by the ECJ. /ends
