My teenage son is learning to drive. Oh joy.
So here we are, my son and I, on a quiet road near our house. There are big red L plates front and back. I am groping through the mists of memory to find useful little phrases like 'Mirror, Signal, Manoeuvre' and 'Handbrake, Neutral'.
"It's all about safety," I say, nervously.
He's already had quite a few lessons, so he's beyond the point of wondering what the clutch is for. But he hasn't had a lot of experience of driving in London traffic. Or of pedestrians wandering out into the road.
At the next corner, wobbling on the edge of the kerb, is a toddler on her bike, her mum anxiously holding on to the handlebars. My son slows to a stop and waves them across.
"No!" I say. "You can't do that! You'll fail your test if you do that!"
(Am I right about this? I think I am. I think you're only allowed to make hand signals specifically mentioned in the Highway Code.)
We set off again, and I say, "I know it's hard when you see other drivers waving their arms around. But no hand gestures."
My son shoots me a look.
"Especially not that kind," I say.
"Really?" he says.
"When you're driving a car," I say, with a saintly expression, "you must never, ever lose your temper. You must be calm at all times."
At the next junction, just as the lights go green, my son stalls. In the anxiety of the moment, he can't re-start the engine. Behind us, a car leans on its horn. I swing round furiously.
"Can't you see?" I shout, shaking with rage. "He's a learner driver!"
The car starts.
"Chill, Mum," says my son, grinning.
Cheeks pink, I wait for my heartbeat to return to normal.