On Friday, June 11, 2021 at 2:24:42 PM UTC+1, wrote:
inside the ceiling switch the red wires were joined and the
blacks went to the switch (one of them had red sleeving on it) resulting
in neutral switching and a permanently live feed to the light! I'm
getting a bit blasé in my old age so this near miss is a good reminder
to check!

I've come across the same thing in the past. About 10 years ago my sister-in-law asked if could change the bulb in their outside porch light. I turned the wall switch off and proceeded to remove the old bulb and received an electric shock. Turns out the previous owner had fitted the light and switched it on the neutral!