if its mildew then yes: take everything off that you can sometimes you have to undo some screws. the spray with dettox mildew remover (its in a light green spray gun bottle) sray it on leave about 3-5 minutes, give it a scrub, leave a bit longer, the wash in your washer with persil bio. Leave in the sun to dry as this kills any remaining spores.
If you can't take the seat off, spray as usual and then scrub as above and wash by hand with persil and a scrubbing brush and very hot water and hose down in the garden (or use a bucket if you are banned). It is important it is rinsed thoroughly as the dettox mildew remover is very potent, very caustic stuff and mustn't come i nto contact with baby.
I have used this cleaning agent on all sorts: caravan tarpaulings, pushchairs, patio furniture, shower etc and even the front of a tea shirt that got put at the bottom of the washing basket with banana on the front.
hope this helps.