In reply to rockwing:
I'd use nikwax or whatever and the hottest water you can stand with washing up gloves on and give it a soak in the sink or bath. Use a stiff brush to get rid of the mould as much as possible. White vinegar then to kill off the rest and rinse after its had a soak in that then reproof.
If that doesn't work then I'd try the washing machine in a mesh bag as above.
Oh and if possible at this time of year some sunshine will do it good as well.
Post edited at 17:38