A FEW weeks before the referendum on the UK’s membership of the EU, this newspaper was among those that warned about the possible economic consequences of voting to leave. It was clear, we said, that should the result be Leave, there would be uncertainty for years to come, a depressive effect on the economy, and potentially serious consequences for that other union –the one between the countries of the UK. Many others warned of the same risks, dismissed as we know by Leave as Project Fear.

A few weeks on, we now see the consequences coming to pass, still accompanied by the same assurances by the Brexiters. One of their number, the Transport Secretary Chris Grayling, said at the weekend that he was not concerned that the negotiations between Britain and the EU could go the way of the talks with Canada. We will have sensible trading arrangements, he said, and he was convinced there would be tariff-free trade because it is in the interests of both sides.

The reassurances are not convincing, not least because the Canadian negotiations have been so difficult, but also because of the gulf between what the Hard Brexiters want and what the EU is prepared to offer. The most committed and hardcore of the Leavers in the UK Government seem prepared to sacrifice membership of the single market to regain control of immigration, while also reassuring us that the EU will do a deal. But the position is clear: full access to the single market means freedom of movement of people.

The possible cost of life outside the single market has also been laid out by the think tank Civitas, which says British companies will face a £5.3 billion bill every year if Brexit means leaving the customs union without an alternative free-trade deal. Civitas points out that the European exporters also have a great deal to lose without free trade, but the potential risks should not be waved away by the Brexiters.

The potential political consequences within the UK also have to be taken seriously. Sadly, the Government still seems determined to resist calls for a vote in the Commons before the triggering of Article 50, even though the convention on the matter is clear – on important questions of foreign affairs, the Commons must give its approval.

On the other question of the involvement of the devolved governments, the UK Government does appear, on the face of it, to be open to discussion. Theresa May and Nicola Sturgeon will have their first Brexit meeting in London today; the UK Government has also offered a new official forum, to be chaired by the minister for Brexit David Davis, that would involve representatives of all the devolved administrations.

But the risks are clear. The Brexit vote has created a democratic deficit in which Scotland faces being part of a decision it did not vote for, so it must be part of meaningful discussions about what kind of Brexit will happen. In particular, the PM must listen to those in Scotland and elsewhere warning about the consequences of Hard Brexit. It could lead us into years of economic disaster. But it would also precipitate a serious and perhaps fatal constitutional crisis for the UK.