British Prime Minister Theresa May | Neil Hall/EPA

The emergency siren is whirring, but few are taking much notice.

The most fundamental Brexit truth right now is this: Unless there is a concession from Brussels over the next few months, a full-blown political crisis in the U.K. is inevitable.

And right now, that concession is nowhere in sight.

That is the reality facing Theresa May as she prepares for the most important Cabinet meeting of her premiership at her Chequers country retreat on Friday, where she hopes to forge a consensus on the government’s preferred future relationship with the EU after Brexit, which could form the basis of a breakthrough in the negotiations with Brussels.

All signs suggest it will involve a lot of British give. But without any EU take it will be pointless.

Fundamentally, both sides have until March 29, 2019 to sign a withdrawal agreement which settles the terms of the divorce and sketches out “a framework” for what the future EU-U.K. relationship will look like.

In that document, there must be a binding “backstop” clause which sets out a series of measures ensuring the border between Northern Ireland and the Republic stays open.

This clause must be legally enforceable “unless and until” a better solution can be found — i.e. it could last forever. Even more importantly, it must also be “Northern Ireland-specific.” In other words, it can’t apply to the whole of the U.K.

If Brussels does not relent on this second point it means that for the U.K. to reach a deal with the EU — any deal — it must sign a legally enforceable treaty binding part of its territory (and not the rest) to EU rules in perpetuity.

The EU’s position means…