Quote:
"All mushrooms are best used on the day of purchase, although cultivated ones will keep for up to three days in the refrigerator. Mushrooms will sweat if stored in plastic, so keep them in a paper bag, or wrapped in kitchen paper.
To freeze mushrooms, slice them and either sauté in butter or oil, steam or blanch. Cool to room temperature and pack in rigid containers. Cook from frozen unless stir-frying, when you will need to thaw them first in order to avoid being splashed by hot oil when you add them to the pan"
Source:
http://www.bbc.co.uk/food/mushroom