Damp found in bathroom corner - how serious is this?

Found a small patch of damp in the corner of the bathroom during my monthly check. Damp meter is reading around 28% in a patch about the size of my hand. The wall feels slightly soft to the touch. How worried should I be? Is this a "call a professional tomorrow" situation or a "try to dry it out and monitor" situation?

28% is definitely into "needs fixing" territory - that's beyond just a bit of condensation. The soft wall is the bigger concern though - that suggests the damp has been there a while and the wallboard is starting to degrade. I'd get a professional damp survey done sooner rather than later. A small repair now might cost £200-300. Leave it 6 months and you could be looking at a much bigger (and more expensive) job.