Theresa May's first Brexit row

So that historic moment tomorrow when Theresa May starts negotiations to take us out of the EU is the moment when we move out of the phoney war over our future relationship with the EU into the real argy bargy.

And the battle lines in the first difficult conflict have already been drawn - as our former man in Paris Lord Ricketts rightly pointed out to me.

There is an important disagreement between Theresa May and the chief negotiator for the EU Michel Barnier: she will say tomorrow in her letter to other EU government heads that there should be simultaneous negotiation of how much we owe the EU in unpaid budget liabilities and also a future trade deal with the EU; Barnier is adamant that we cannot talk trade till we agree what we owe, and that demand for cash upfront will be enshrined in negotiating guidelines to be issued by EU president Donald Tusk at the end of the week.

Barnier's position is anathema to May: it is politically impossible for her to pay a bean to the EU, let alone the €30bn to €50bn they want, in the absence of some certainty for British businesses that they will continue to get privileged access to EU markets.

It is a proper standoff. And it is not at all clear where the compromise can be found.

Gawd - we've got years of this ahead.

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