When I joined the Foreign Office, 40 years ago this autumn, there were rules about the cars diplomats were allowed to buy when they were posted abroad. As far as possible, British cars must be chosen.
So the ambassador should fly his Union flag from a Rover 3.5, while the head of chancery made do with an Austin Princess, leaving the third secretary to impress the natives no end with his Riley Kestrel.
But in those benighted lands where British Leyland car dealerships were unknown, or where only a limited range of Rollers and Land Rovers was available, you could instead buy local. What you couldn't do was drive a Merc in DC, or a Beemer in Toronto.
I often recall this tactful requirement as I cycle round central London on the Brompton and am cut up by self-important ambassadorial chauffeurs in their S-Class limos with diplomatic plates. 'Buy British,' I shout at uncomprehending Koreans. ROK 1 is a Merc.
You might think they would buy a Jaguar, if the top of the range Kia isn't impressive enough. PHI 1 might be the Queen's consort's vehicle, I suppose, though that's probably DOE 1 and certainly a Bentley. Why can't the Philippines stretch to an XF, now that these are well suited to chauffeurs and passengers en route to receptions chez the Papal nuncio?
NEP 1 is a Merc, too, and how many Gurkhas are there in the Bundeswehr? A smart Range Rover would do the trick and be ideal back in the Himalayas.
The Aussies do it right, in spite of all their current troubles and our now-routine humiliation of their sport teams. The high commissioner has a very smart Jag attached to AUS 1. Good on yer, sport.
I haven't tangled with the Thai car in London, but on a quick flit to Bangkok I had the leisure to observe the cars the Thais buy. Like most fast-growing Asian cities, Bangkok is a traffic jam for 14 hours a day.
There aren't very many Rileys, I am sad to say, but as compensation you have time to count the Tesco and Boots outlets. Boots has about 300, I gather, including one in the red light district that must do a flourishing trade in family planning accessories. Tesco has more than 1,200.
I confess I didn't count them all. Our Man was a mine of useful information about Britain in Thailand and gives a mean party.
Since I was last in our embassy, the Treasury has forced it to sell off part of the garden, but the statue of Queen Victoria is still proudly on display, and there is still a punkawallah who operates an elaborate system of fans on the ceiling of the dining room like a set of clipper sails, with a complicated pulley mechanism running through to the kitchen. It is a shame that no one dares to smoke a cigar these days.
There are no direct flights yet from Bangkok to Wroclaw: it is a route Ryanair has unaccountably neglected. So I had to pop into London on my way there for a wedding. It was a Polish-Norwegian union, which seemed pretty exotic to me until the groom's dad told us he had made enquiries and discovered there are about 200 such alliances a year. Poles and Norwegians do, of course, have one hobby in common and, between them, a remarkable number of different ways of saying 'cheers'.
So I don't recall much about my flight home the next day, but before the marriage ceremony I had the opportunity for a quick look round. Germans, and people like me whose history course ended in 1939, know the city better as Breslau, though that is a name not mentioned in the local museum.
The Catholic Cathedral of St Mary Magdalene is a little more forthcoming, noting that the building had been a Lutheran church from 1523 to 1945. Most of the current population were moved there from what is now Belarus, or the Ukraine, after the war. They have made a decent job of sprucing the place up, at least since 1989.
The visit allowed me to confirm that there are still a few Poles left in Poland, rather than in Ealing or Sandwell. But, boy, do they like flying back and forth to visit Mum! In 1989, when those gloomy generals were still in charge, there were little more than 200,000 seats a year on flights between the UK and Poland.
Now the figure is close to 6 million, most of them on Wizz or Ryanair. Michael O'Leary must genuflect daily before the patron saint of Poland, whoever that might be.
Manchester was a bit of a comedown after these excitements. It was recently voted the most vibrant city centre for students, even above London. I won't hear a word against my home town, but you have to wonder what these surveys are measuring.
If we're talking about the price of cheap lager, then I grant you that Covent Garden is not the place to seek it out. And if, like me, you come over all peculiar just at the sight of the Colin Bell Stand at the Etihad stadium, Manchester evidently has some trump cards.
But the Arndale Centre isn't quite Bond Street, or even Westfield. There is, however, the famous curry mile, which offers perfect accompaniments to eight pints of lager. Perhaps that's what the survey meant.
Of course, soon there won't be any need to compare London and Manchester for a night out, as all these delights will be 20 minutes (or whatever it is) closer to the rest of us, for the modest cost of a new £42bn train set. I don't know why ministers don't major on that point when they try to sell the idea to a sceptical public.
Howard Davies is chairman of the Airports Commission.
Follow him on Twitter: @howardjdavies