I have had good luck with the compounds they sell for removing black algae from swimming pools or spas. Some work with just a teaspoon full per gallon of water, or some make a paste that you can spread on really stubborn outbreaks. Make sure you check a small spot first if there are colours or fabrics that might suffer.
Here is a link to some information that may help (USA products but).
Sainsburys sell a spray on "Mold and Mildew" remover I use it on PVC cushion covers and non fabric sufaces, it works very well,spray on leave for about 10-15 minutes, rinse off. Be sure to wear protective gloves. Trevor