For months now, at least since Theresa May addressed the Conservative party conference last October, it has been clear that Britain is heading inexorably towards a hard Brexit. In that speech, the prime minister described what it would mean for Britain to be "a fully independent, sovereign country" after it leaves the EU.
“We will decide for ourselves how we control immigration. And we will be free to pass our own laws,” she said.
In the language of the EU, this means an end to the free movement of people and that the European Court of Justice (ECJ) will no longer hold sway in Britain. Either of these red lines would have made membership of the single market unlikely; together they rule it out altogether.
British ministers have been more ambiguous about the likelihood of remaining in the customs union, perhaps because they disagree amongst themselves about it. But May’s appointment of a secretary of state for international trade offered an early hint about her own intentions, because membership of the customs union precludes the negotiation of any bilateral trade deals.
Exultant
Foreign secretary Boris Johnson was exultant on Monday after Donald Trump said he was willing to conclude a US-UK trade deal without delay.
"It's great to hear that from president-elect Donald Trump. Clearly it will have to be a deal that's very much in the interest of both sides, but I have no doubt that it will be," Johnson said.
Britain's departure from the customs union is the biggest single obstacle in the way of avoiding the return of a hard border on the island of Ireland. The hard border has only ever taken two forms – one for security during the Troubles, and the other for customs checks before Britain and Ireland joined the common market.
Politicians in Britain and Ireland have suggested that technology might make customs checks almost invisible but no such border currently exists anywhere. Even along the border between Norway and Sweden, one of the most technologically advanced and co-operatively managed, goods must be cleared for customs and lorries are checked as they cross from one country into another.
Pound shop
May is unlikely to offer many specifics on Tuesday about her approach to formal Brexit negotiations, which are due to start before the end of March. But the foreign diplomats who will be her audience at Lancaster House will be as alert to the tone of her remarks as to their meaning.
Philip Hammond, her chancellor, threatened this week to turn the British economy into a kind of pound shop on the edge of Europe, cutting taxes, regulations and workplace standards, if the EU did not grant it market access after Brexit.
His remarks were hailed in Britain as a welcome sign of swagger ahead of the negotiations but it cut little ice in Europe, where German MEP Alexander Lambsdorff suggested that the best response to such threats were "to calmly ignore them".