I'm in work an hour early today, as partial compensation for the fact that I have to leave two hours early to go home and wait for a boiler engineer.

Of course, it so happens that that's also the time I'd have shown up if I'd failed to notice that the clocks had changed. Naturally this occurred to me; naturally I suspected that somebody would make that assumption; and naturally, as I was sitting down at my desk, someone did indeed ask ‘You know the time changed, didn't you?’.

In such situations I can think of no better response than the QI alarm sound. (Though Stephen Fry pulling a foolish face is optional.)