BBC News has published an intelligent and even-handed explanation of the Irish border backstop provision included in former UK PM Theresa May's Withdrawal Bill (which Parliament 3 times failed to approve).

The backstop continues to be a controversial issue because both frontrunners for the UK PM position - Boris Johnson and Jeremy Hunt - have said that they intend to eliminate the backstop from a new withdrawal plan to be accomplished in October 2019 (Johnson) or possibly later (Hunt).

The most recent definitive EU statement on the backstop came from Chief Brexit Negotiator Michel Barnier in an interview in March when he said that the EU was prepared to give the UK assurances that the backstop is intended to be a "temporary measure" to be used only in the case of a "worst-case scenario" (i.e. no-deal Brexit) but that there should be no time limit attached to the backstop provision.

And in February, European Council President Donald Tusk - speaking in Brussels alongside Irish Taoiseach Dr. Leo Varadkar - appeared to say that the EU is not open to any further negotiations in regard to the backstop.

Elimination of the backstop - and any customs union between Ireland and Northern Ireland - would almost certainly result in a return to a customs border between the 2 countries, which would be a terrible blow to tourism and agriculture in both countries, and could undo the Good Friday Agreement of 1998 between the British and Irish governments which largely ended sectarian violence in Northern Ireland and the border area.

Please read the BBC analysis.