“Why, sometimes,” the Queen said to Alice, “I’ve believed as many as six impossible things before breakfast.” The Tory leadership candidates seem to have been particularly busy before breakfast. Between them they have come up with a veritable Wonderland of wheezes to resolve the Northern Ireland backstop issue. Insert a time limit or an exit mechanism. Set up a border council. Expect the EU to trust in technological solutions before they have been discovered. Change the UK’s negotiating team. Conjure up Angela Merkel riding to the rescue. Crash out of the EU and pretend the problem doesn’t exist. Even a respectful stratagem to pay Ireland for the technology. Stage direction: doff cap. God bless you, sir. Unfortunately, comprehension levels about Ireland have slipped back somewhat since Queen Elizabeth’s state visit to Ireland in 2011.

Many of the candidates are very decent politicians who I have no doubt mean well. However, with the exception of Rory Stewart, they are offering a variety of fictions in relation to the backstop. We understand that politicians make promises when they face elections. However, in this case, the harsh reality that beckons if only illusory avenues are explored is a no-deal Brexit. I sincerely hope that the candidates still seriously in contention leave themselves enough wriggle room to avoid the very outcome they would prefer to avoid.

Like most Irish people, I have immense affection for Britain and its people. It is better for a friend to be honest than to nurture false hopes. “Let’s not talk falsely now, the hour is getting late,” as Bob Dylan might say. In that spirit, as an antidote to the illusions that have characterised the hustings so far, I would offer a modest Irish breakfast consisting of half-a-dozen simple facts.

First, the backstop is an essential element in preserving the balances of the Good Friday agreement. It is not a tactic. It is not a ruse to advance Irish unity; only a hard Brexit would achieve that. Some argue that because the border is not prominent in the explicit wording of the Good Friday agreement, it is not central to the agreement. That is like saying that because the agreement doesn’t refer to fresh air the people of Northern Ireland don’t need to breathe. The deepening of relationships on the island of Ireland is one of the core principles in the equilibrium of the agreement.

Second, our European partners designed the backstop because successive British and Irish governments have spent decades explaining to them the complex and subtle balances that brought peace to our island. They are aware that a majority of people in Northern Ireland support the backstop.

Third, the EU will also continue to insist on the backstop because the single market, which the UK did more than anyone to shape, is based on laws that necessarily distinguish between countries that belong to it and those that don’t, and on rules that regulate the trade between them. The avoidance of a hard border requires not the hypothesised good intentions of future British governments but detailed practical arrangements for which, thus far, the only identified template is the backstop.

Fourth, the backstop is an insurance policy. No more but also no less. It can be superseded by the future UK-EU relationship or replaced by alternative technological arrangements if and when identified. But an insurance policy ceases to be an insurance policy if it can lapse while the risk it is designed to mitigate is still live.

Fifth, the most important reality is that the EU will not renegotiate the backstop. EU leaders could not have been more consistent, more clear or more united. Pretending or praying that this were otherwise is worse than wishful thinking. It is a highly dangerous obfuscation that muffles the sound of the clock ticking towards no deal. If the UK were to crash out and then seek to discuss its relationship with the EU, first up would be the withdrawal agreement issues including the backstop.

Finally, the EU’s approach to a new British prime minister will be characterised by courtesy, respect and good faith. Even as the temptations of a Tory party conference beckon, a new prime minister should reciprocate. But the difficult compromises in the withdrawal agreement reflect interests not personalities. A prime minister looking for new concessions would be no more credible than a new European commission seeking to double the calculation of what the UK owes to the EU. The deal is done. On the separate matter of the future relationship, the EU will respond constructively to the UK government’s evolving approach.

When Alice asked the Cheshire Cat for directions, it told her “that depends a good deal on where you want to get to”. Most of the candidates in the Tory leadership election want to get to a Brexit deal. They should avoid directions that would take them over the cliff.

• Bobby McDonagh was Ireland’s ambassador to the UK from 2009-13