If it's a sunny day, put it outside in the sun for as long as possible. Then always use a waterproof cover. Those washable, cotton-covered latex mattress covers are good. They take a while to dry though so you might want two.
A new definition of what constitutes British


. How do we save the mattress? Up to now, I've soaked it with plain water and put a towel on top to soak the water up!