Single duvets can go into the washing machine; check the label for instructions. Any duvets larger than single normally need to be taken to the launderette but some modern machines have a very large capacity, so check first. As long as the item goes into the drum easily and there’s a bit of space between the duvet and roof of the drum, you’ll be fine.
Either pack away in a spare suitcase, lidded plastic boxes, zip-up plastic bags or those storage bags that hook up to the vacuum cleaner hose to extract air and create an airtight seal (they reduce the volume to about 50 percent, are available cheaply from Argos and can be reused). Fold or roll clothes and wrap in acid-free tissue paper to prevent creasing. When your case, box or bag is full, sprinkle the top with rosemary, lavender, bay or pieces of cedar to deter moths and other unwelcome critters. Store either on top of the wardrobe, in a drawer under the bed, in a spare room or dry loft.
If you think have a moth problem, vacuum and wipe out the wardrobe and drawers with soapy water, getting right into the corners. Make sure you clean carpets and floors, especially under furniture and along skirting boards. And as soon as you have vacuumed, empty the bag or canister so they don’t breed in there.