Looking back, the crackdown must have started on Monday three weeks ago. That day, Li Zhe was late for an appointment. He telephoned me apologetically to say he was having some trouble. The policeman whom he regularly passed on the way to work had confiscated his bicycle. It did not have the little yellow licence plate showing it was properly registered.
Li Zhe's bicycle had actually been without a registration plate for months, and he soon found out why he was stopped that morning.
The police had launched a campaign against non-registered bicycles. At the district police station the officer sighed and said, "I've had 130 people in here looking for a new bicycle licence in just two days."
The police drive was not, it soon became clear, directed solely against unregistered cyclists. A few days later when walking along Jianguomenwai Road, I saw the hawkers squatting on the pavement suddenly cram their wares into hold-alls and disappear quickly into the crowd of pedestrians. I looked around. Crawling ominously along the cycle lane behind us was a blue and white patrol van carrying officers from the discipline unit of the Beijing Municipality Comprehensive Administration Office.
This unit has recently got very active on the Beijing scene, chasing away pedlars and giving out parking tickets. One of the compensations of driving in Beijing has always been that away from big intersections, drivers could leave their vehicles pretty much where they liked. Suddenly that is no longer the case.
A blizzard of parking fines has descended on car windscreens all over the city. The Beijing Evening News reported recently that in one day the police handed out 30,000 tickets in two hours, and that in a week they towed away 12,000 vehicles and imposed 220,000 fines.
The police have also been pulling in motorists who violate driving regulations on the capital's usually chaotic streets.
Beijing drivers are cyclists at heart and they tack and weave as if on two wheels. Extra police have now stationed themselves at crossroads, waiting to pounce on the slightest infringement. A new, slick, generation of male and female patrol officers has appeared, cruising around on fast new motorcycles, geared up like American cops.
Of course, I should have known what was behind all this. Beijing enforces street clean-ups and good behaviour on big occasions. We had something like this at the time of Deng Xiaoping's funeral in March and during the celebrations for Hong Kong's return to the Motherland in July.
Now it's the big one, the week long 15th Congress of the Communist Party, which is being held in the Great Hall of the People and which is trying to figure out why state enterprises aren't doing well.
The order has gone out that the capital must look its best and be on its best behaviour. And it coincides with a long-planned push to upgrade Beijing's traffic discipline.
This has been publicised through banners and notices declaring: "Farewell to uncivilised driving habits"; "Create a good law-abiding environment", and "Don't park or drive illegally".
City road users are in a mutinous state. A taxi driver working for the Beijing Auto Service Company complained bitterly that they were all losing money. "Since July we have had to go for long study sessions twice a month on `the new spirit of rectifying traffic'," he moaned.
"The police have got really tough. Normally you pay a fine of 50 to 20 yuan (£4 to £16) for illegally overtaking or whatever. During the period of the congress they make you pay the maximum 200 yuan for everything, and they keep your licence until it's over. And then you have to pay another 500 yuan to the company because they get fined as well. And that's a week's wages."
He was grateful at least that the contract for ferrying the 2,000 congress delegates around town had gone to a rival taxi firm, the Capital Auto Company, whose drivers have to attend traffic awareness sessions four times a month.
That job was a real money-loser. The drivers had to wait for the delegates when they went shopping or for meals and couldn't take other fares.
So what did he think about the big slogans all over town saying "All Beijing welcomes members of congress"? His reply was unprintable.
Li Zhe got his bicycle back because he explained that the registration plate had been stolen and he still had the receipt.
"Why did the thief not steal your bicycle as well?" I wondered.
"Because it is eight years old and a real wreck."
"Why not buy a new one?" I asked, knowing he could afford it.
"Because then the bike might be stolen," he replied.
There was no answer to that. But it might help congress delegates understand why at least one of China's troubled state enterprises - which makes bicycles - isn't doing as well as it should.