When he thinks dark thoughts about Europe, David Cameron may worry about losing control of immigration, or excessive regulation preventing banks in the City of London from setting Libor to suit their convenience.
My major concern, which can be guaranteed to make me think warmly about Nigel Farage, is the seat numbering system in eurozone theatres.
Explaining the problem may tax my verbal skills, so let's take a simple example. You arrive at the Comedie-Francaise having prudently purchased two tickets online for yourself and your lady wife or mistress, as the case may be.
The box office apparatchik hands you, say, seats E12 and E14. Zut alors, I hear you expostulate, surely some mistake? We will have a native interposed between us. How embarrassing for him and her to be sandwiched between a couple of rosbifs, and how constraining for you. Suppose the romance of a weekend in Paris inspired you to hold hands?
But you would be wrong to worry. French theatres, and others on the continent, operate a numbering system that divides the house down the middle, with an odd side and an even side. So E12 and E14 are side by side, and you may hold hands, or any other piece of your partner's anatomy, with gay abandon.
The purpose of this counter-intuitive scheme is not immediately apparent. It may minimise the risk, in an aisle-less theatre, that a fat bloke with E36 might have to push past 35 patrons, having mistakenly started his journey at E1.
With an odds-and-evens system, the maximum number of glasses his posterior can dislodge en route is halved. But the same effect can be achieved with a sign telling the holders of seats 1-18 to bear left, and those with numbers 19-36 to hold hard to the right as they enter the auditorium.
I sense I may have lost some of you here, so let me cut to the political chase. A recent weekend in Stockholm threw up the fascinating information that the Swedes do it the English way. No odds-and-evens nonsense for Ingmar and Greta.
If you were unlucky enough to have seats E12 and E14, one or other of them would indeed be between you. And very charming they would be about it, too.
The Swedes sensibly used to drive on the left within living memory (well, until 1967, at any rate, which seems like yesterday to me) and are also, of course, like us, not in the eurozone. I used to think they wanted exchange rate flexibility, but now I suspect the thought of having to renumber all the seats in the Opera House is the decisive factor.
I can't wait to go to Prague to find out if Czech euroscepticism is also associated with rational seat numbering.
Otherwise, Stockholm is everything you expect it to be: beautiful, unspoilt, scrupulously clean, with lots of herring, almost excessively polite staff all speaking better English than my children, and ruinously expensive - it cost £9 to check our overcoats at the Opera House.
But we were shocked to find there was litter. In three days I must have counted almost a dozen items. Have the Swedes changed character and lost interest in their tidy environment? No, indeed. Almost all the offending items were Russian cigarette packets. (In case you think your correspondent is losing it, I should point out that it was icy underfoot and you were well advised to watch carefully where you put your Clarks.)
Stockholm in January is invaded by Russian tour parties in dirty buses belching smoke (and that's just the passengers). I suppose that in the same way that the Swedes hop down to the Canaries for some sunshine, they find Stockholm in the winter to be a nice warm change from Moscow.
But they don't seem to be particularly cheerful at zero rather than minus 15. Even the thought of being joined by Gerard Depardieu and Brigitte Bardot hasn't made them smile.
They march around austere royal palaces looking bored and disapproving, especially at the fact that they can't smoke inside. No doubt the terrifying price of vodka and wine in Scandinavia doesn't help their joie de vivre.
As you might expect, the Swedes are a bit less deferential to their royals than we are. You can tour the apartments of the palaces they use when the king and queen are in Gstaad, or wherever they go to ski.
In the guest apartments of their Stockholm pad, a cheery attendant, overhearing us talking about the gloomy furniture, told us we were looking at the beds that Charles and Camilla had used last summer. We weren't given any more intimate details.
In Sweden, a Freedom of Information request would probably yield something more, but best not to think about it.
Overall, Sweden is astonishingly familiar. They eat a bit more black bread than we do, have much less tiresome security, and their principal airport has three runways. Otherwise, you might be at home.
So, even though they share our suspicion of the euro, why is there no UKIP-like SWIP agitating for withdrawal from the EU? Because the Norwegians, the old enemy, are out? I doubt it.
They just seem content to be both Swedish and European at the same time, a trick of a kind that we do not seem to be able to pull off.
So when we sail off into the middle of the Atlantic in an attempt to avoid the Working Time Directive, they will wave us a sad goodbye, but remain in the club - at least until an EU Directive on Theatre Seat Numbering is hatched in Brussels.
You wouldn't put it past them.
- This diary appeared in the February edition of MT.