Washing P + T cocoon

[chickabilla]

I was going to use my single pram and buggy board when our new baby arrives in March but our toddler is a menace and I have a long school run with my oldest so we just bought a second-hand Phil and Teds. It has a cocoon but I don't know how to wash it for the newborn. We can't just buy a new mattress like we were planning to for the Quinny carrycot.

Anyone know the best way to clean it?

Thank you!