The London mayor was called to London’s Victoria Park as a “special guest” and took his place to ride along a zip line, having borrowed a hard hat and two union flags.
His descent began well. The mayor plummeted along, smiling and waving his two flags at spectators below.
But around 20m into the ride, he got stuck, and was left dangling from the wire while the audience below laughed and took pictures.
The mayor retained his humour, kicking his legs around and saying: “It’s very, very well organised.” He then said: “Get me a ladder!”
Eventually, two assistants appeared armed with a rope and pulled him along. As they did so, Mr Johnson shouted: “Here we go! Ici nous allons!”
Afterwards, he described his experience, saying: “It was wonderful, I thoroughly recommend it. I wouldn’t want to have been up there all afternoon. But loads of people are going to enjoy it.
“I don’t know [how I got stuck], I seemed to turn round, and possibly what had happened is they left a brake on or something, I don’t know. But it was wonderful, I’d thoroughly recommend it.”
A spokesman for Mr Johnson said that he “remained unbowed” by the incident, adding that had Olympic judges been watching, they would have marked him down “for artistic interpretation”.
“Unlike Team GB, he won’t be bagging any gold medals today, but he remains unbowed,” the spokesman added.