Black mould keeps coming back on my bathroom ceiling — how do I get rid of it for good?

You're playing whack-a-mole because you're treating the stain, not the cause. Two things are working against you:

1. Moisture + no ventilation. Hot showers dump steam, and with no window and a weak extractor it sits on the cold ceiling and condenses. Keep a surface damp for 2–3 days and mould colonises — our climate makes that easy.
2. Gypsum board loves mould. The paper facing is basically food for it. Once mould has gone into the board, wiping the surface does nothing — the colony is inside, so it comes straight back.

How to actually stop it: - Fix the air first. Make sure the extractor genuinely vents outside, not just into the ceiling void — a lot of them don't. Run it during the shower and 20–30 minutes after. If it's feeble, replacing it is the single most effective thing you can do. A working AC that dehumidifies helps too. - Small, surface-only patches: treat with a proper mould remover (not just bleach-and-wipe, which fades the colour but leaves the roots), let it dry fully, then use a mould-resistant primer and paint. - If the board is soft, bulging, stained right through, or it keeps returning: that gypsum is colonised internally — it has to be cut out, replaced and re-skimmed. Surface cleaning cannot fix penetrated board.

For the cut-out-and-re-skim on a ceiling that's past cleaning, that's a gypsum and ceiling repair job — but honestly, sort the ventilation the same week or the new board goes the same way. If the trigger is a leak from above rather than shower steam, see our ceiling water-stain thread first.