The coachload of Chinese students who were decanted into Greenwich Park on Christmas morning to visit the historic observatory must have wondered at the eccentricities of the English.
Not only was Santa Claus jogging through the park (or at least a man wearing a red and white coat over his shorts, a Santa hat and a strap-on beard), but there were two men hitting a tennis ball to each other on the main road.
Traditions are important at Christmas and, like the Serpentine swimmers who refused to allow the frozen river and cancellation of their annual Christmas race to prevent them having a dip, so my father and I were determined to play tennis on Christmas morning whatever the weather.
It is a tradition going back at least 15 years (the last time I let him lose was in 1998) but it appeared that the cold snap in Britain might have broken the run when we arrived in the park yesterday morning and found the four courts covered in white ice.
No matter, we decided to play in the road instead, which was the only surface free of ice. My car marked the line of the net and the gutters formed tramlines. The baseline was a moveable feast but as we decided to dispense with scoring and just see how long we could keep each rally going, it didn't matter.
We stayed out there for an hour, despite the cold weather, batting the ball back and forth and sharing the odd joke with passing joggers and pedestrians, pausing occasionally to allow a car to drive through our court.
It was wonderfully eccentric, which is as it should be at Christmas. Some stony-faced sourpusses didn't understand why we would want to play tennis in the road on one of the coldest days of the year, but most raised a smile. One jogger deliberately hurdled our imaginary net, while Santa, as he jogged past, promised that next year he would leave a net in my stocking.
Most heartening, though, was the man who stopped to chat to us at the beginning of our match and then returned half an hour later with some mulled wine. "I thought you could do with this," he said. And there, in that kind gesture of a stranger to two madmen, is the true spirit of Christmas.