Leo Varadkar (Dublin West, Fine Gael) | Oireachtas source

The Deputy's assessment is correct that it is his view that the United Kingdom should leave the European Union whole and entire, to use his own language. That means the UK, including Northern Ireland, leaving the customs union. However, as I explained to him when we met in New York, there is a reason we came up with the deal we did after two years of negotiations with Prime Minister May and her Government. The backstop provides for a single customs territory. It does not provide for Britain or Northern Ireland staying in the EU customs union; it provides for what is described as a single customs territory. That satisfied our demand and desire that there not be customs checks North and South, but also the concerns and desires of many unionists that there not be any customs checks east-west. A single customs territory was designed specifically to meet that need. That is why we ended up with the backstop and why it is the best solution. Having the entire UK within a single customs territory avoids the need for customs posts North-South and east-west. I explained to Mr. Johnson that we spent two years going up and down all of these rabbit holes and that we came up where we did because we needed a solution that avoided customs posts not only on the land border between North-South, but between Northern Ireland and Britain and between the Republic of Ireland and Britain. Very often those who were not part of negotiating an agreement do not know why those negotiations reached a certain point, but this is why we reached that point.

See this speech in context