There is all this talk about customs work being done without a hard border, but as I understand it this will/would take years to develop.
They'll have to start charging tariffs to goods from Northern Ireland when we come out, so something will have to be done. I predict a lot of criminality/smuggling - possibly in both directions.

But Rees Mogg assumes that the UK won't want to put up hard borders ie it will stick to the Good Friday agreement.