Is Amber Rudd's insistence the UK 'will be leaving the customs union' credible?

Amber Rudd has insisted the UK will leave the customs union after Brexit. Credit: PA

Amber Rudd was forced by the PM this afternoon to put out a statement that "of course when we leave the EU, we will be leaving the customs union", because over lunch with journalists she had allowed some flicker of doubt over whether the second event really is the dawn after Brexit's night.

But every time the government insists that leaving the customs union really is necessary, desirable and inevitable, it sows fear and confusion about two other Brexit statements made by Theresa May that are supposed to have the status of biblical commandments.

These are:

1) That the Good Friday Agreement will be honoured, and the border between Northern Ireland and the Republic will be kept open, and;

2) That there will never be any new border in the Irish Sea between Northern Ireland and the rest of the UK.

European leaders could halt negotiations over concerns about the Irish border. Credit: PA

What the government refuses to accept, with all the furious zeal of a Christian fundamentalist presented with Darwin's "Origin of the Species", is that there is literally no chance either the main EU Brexit negotiator Michel Barnier or other EU government heads will concede the Irish border would be open and permeable in the spirit of the Good Friday Agreement after Brexit unless two major conditions are met.

These are:

a) Either the UK remains in the customs union, while also committing to keep product and food standards permanently aligned with those of the UK, or;

b) Northern Ireland in effect remains part of the customs union and single market while Great Britain withdraws from both.

For the avoidance of doubt, most Tory eurosceptics together with Northern Ireland's DUP - without whose succour May falls - are implacably and religiously opposed to both options a) and b).

Theresa May has so far insisted that technology will solve the problem. Credit: PA

To put it another way, the prime minister's fundamental positions on Brexit are seen as incredible by almost everyone, except those who serve in her cabinet.

This perhaps would not matter and could be ignored, except that come the end of June, EU government heads will at their next summit call a halt to all negotiations on a future relationship with the UK unless progress is being seen to be made on the logistics of keeping Ireland's internal national border open.

It is extraordinary that no member of the cabinet, whether a Brexit ultra or a repenting Remainer (like Rudd), can bring themselves to face the hideous (for them) truth that the prime minister's proposed customs "partnership" and assorted technical and bureaucratic proposals to speed goods across all our borders will never persuade the rest of the EU that they could prevent the re-establishment of a border on the island or Ireland.

The UK is now risking a high-stakes row with EU leaders - and has no time to waste. Credit: PA

That said, they must surely see that the majority of MPs and Lords are closer to EU leaders on whether or not membership of the customs union is necessary than they are to the prime minister - which raises the risk that parliament at some point loses patience with the prime minister and legislates to expose the internal contradiction in her Brexit principles.

Every time a Rudd or a May says "we are leaving the customs union" I have no doubt they mean it.

But each repetition brings the UK closer to a negotiating car crash with the EU, and an associated constitutional car crash in Ireland.

Whether she is conscious of it or not, the PM is playing the highest stakes game of chicken. Is there any good reason to believe Merkel and Macron will blink first?