1. The UK has signed an international treaty (The Good Friday agreement) with Ireland which states there will never be a hard border between NI and Eire. There is no end date to the agreement. The UK is in the agreement in perpetuity and cannot withdraw unilaterally. The UK can only get out of the agreement with Ireland's (and the people of NI's) agreement.
There is no such provision in the Good Friday Agreement (written or implied) that prohibits a 'hard' border between the Republic of Ireland and Northern Ireland, neither is there any provision mandating or encouraging a 'soft' or invisible border. In fact there is nothing specific in the GFA about the border between the Republic of Ireland and the United Kingdom.
It's arguable however that to erect checkpoints at the border whether by the British Government or the Republic of Ireland Government would contravene the spirit of the GFA. That's all.
3. The EU says "Tell us what you are going to do about the border to ensure there is no hard border. It isn't our problem, it is your problem because you have chosen to leave. If you don't leave, there is no problem".
This is where things have got a bit muddy, as it's true that by leaving the European Union, the United Kingdom has created a problem. However strictly speaking it is not the UK's problem but a problem for the Government of the Republic of Ireland and the European Union in how to interpret and enforce
their laws on
their side of the border. Once the United Kingdom has left the European Union, EU law will not apply and it shouldn't be for the UK to work out how EU law can be enforced in an EU state.
I was listening to
Any Questions on Radio 4 last night and they were talking about the border and the backstop. Dimbleby asked Hillary Benn who will erect the border posts?, given that the EU, RoI, and the UK have said that they will not. Predictably Benn answered with a lot of waffle along the lines of
The EU says this.... The EU says that.... EU law.... blah blah blah , but he didn't actually answer the question and I thought that it seems that many of these politicians and commentators are in thrall to the EU and while it's clear that they are not in favour of BREXIT, it's also clear to me that they don't seem to
'get' that we will no longer be subject to to laws, rules and regulations of the European Union. Stockholm syndrome springs to mind.
4. Consider animals. EU law states that any animal crossing an EU border must be inspected unless it comes from somewhere which applies the EU laws relating to animals. So animals can cross the France-Belgium border freely.
5. Some NI farms straddle the border and animals roam freely across the border.
There are already veterinary checks between Great Britain and Northern Ireland and it would be sensible to maintain these, but as said earlier applying the whole body of EU law to Northern Ireland does contravene the GFA as it alters the status of Northern Ireland without the consent of the people of Northern Ireland.
The whole issue of the border on the island of Ireland has been inflated by the EU into this huge insolvable problem that can only be solved by the effective annexation of Northern Ireland from the UK. In my opinion the British government have been complicit in this deception to make it seem that leaving the European Union is too hard and to have another referendum. It seems likely to me that they will succeed.