THESE columns exert themselves to cover a broad range of topics, but that range never before went the length of Scottish seed potatoes, of which a year’s mature crop has long been produced and turned into chips and crisps for the whole of Europe. No longer!

In essence it is a vegetable equivalent of another great delicacy, the deep-fried Mars bar. That makes it worthy of an equally honoured place in our national cuisine, worthy also of the appreciation it has long enjoyed from continental consumers of pommes frites or patatine, delicacies all ultimately owed to our generous northern soil.

Now, under the Brexit deal signed by Prime Minister Boris Johnson, these terrific tatties may without further ado be excluded from European markets, worth £112 million a year. They will be victims of the new order in trade that the UK and the EU are to start constructing next year.

From January 1, 2021, the generous freedom for divergence under the existing rules will cease. In the new order, according to the official explanation, “there is no agreement for GB to be dynamically aligned with EU rules”, and so free trade in seed potatoes must come to an end.

The question naturally arises how the British side failed to represent the producers’ interests effectively. OK, this trade may be obscure, and unlikely to make headlines in England’s chauvinist popular press. Even so, going beyond the shrill verbiage, these are real businesses and real workers that are going to be damaged, finally in the shape of bankruptcies and redundancies.

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Whitehall’s negotiating team would never have dreamed, for example, of just ignoring the much more powerful whisky distillers. Probably it’s because the potato seed farmers are so unglamorous that the political risks of adverse publicity can be ignored by the Government.

It is also a good example of how much better things would have been for the victims if Scottish rather than UK ministers and civil servants had represented them. The world of policy-making in Scotland is a small and cosy one, where all key figures on the lobbying and on the official side know one another and meet regularly.

It would be inconceivable for a particular sector to be forgotten, Yet that is obviously easy enough in the UK system, where the contacts are much looser and interventions from Scotland are not welcome anyway. We may expect more of this during the years ahead as a new European trading system is elaborated.

That appears to be the message also from a second major part of the Brexit deal. Again of special concern to Scotland is the agreement on fishing. Since before the time the UK entered the EU, this has had a Common Fisheries Policy.

In principle all member states have enjoyed equal access to all fish in all European waters, though in practice many special arrangements were made in particular cases and especially with the needs of conservation in mind.

Over the years, the basic structure caused the policy to develop in ways peculiar to itself. Scots fishermen, hard hit by the opening of our waters, found out how lucrative shellfish could be, especially in European markets.

Lobsters, prawns, oysters, scallops and so on let them recoup some part of their losses elsewhere. They left behind the sorts of fish that are more often consumed in the UK market, the cod and the haddock, to be caught and sold over here by boats from other countries.

So a point has been reached where Europeans eat the fish we catch, while we eat the fish Europeans catch. It’s quite a neat arrangement, but unfortunately it’s coming to an end this Friday.

The common policy will cease to operate not because of any positive decision but because it will simply no longer apply after the UK, which has the biggest European fishing industry, leaves the EU. There is a further period of transition lasting five years, but what comes after will need to be negotiated. We are all back to square one.

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Although the Scottish Government is pro-European, it has been acutely aware how hostile to the EU the Scottish fishermen have always been. Ministers say airily that all these things can be sorted out once an independent Scotland comes to negotiate its re-entry to the EU.

The trouble is that in Brussels they do not see the common policy as up for renegotiation. It has been a European policy, and not in any way national policy, ever since we went into Europe in 1973, and now it is not going to be handed back to the member states.

The last time the Norwegians tried to enter the EU, in 1978, they wanted concessions on fisheries and Brussels refused. So the Norwegians stayed out. It is not likely Scotland will be treated any differently.

Everybody has got fed up of the four wearisome years of negotiation that have led to this Friday’s parting of the ways. But the agreement now reached does not in fact settle all the outstanding questions, and the agenda for the talks due to take up the next five years is already a full one.

In Scotland it is quite likely negotiations with or about Europe will extend even beyond that, and become perhaps a permanent part, even the main part, of both our foreign and domestic policy.

We had better be more prepared than we are now.