Condensation, not spillage, is the usual cause
A London bedroom is often the smallest room in the flat, with retrofitted double glazing and no trickle vent. Overnight moisture has nowhere to go and settles into the ticking and the top of the fill.
That shows up as grey tidemarks along the edge piping and a musty note when the duvet comes off — which is extraction and airflow work, not something a spray-on freshener will fix.

