Just bought a Mahle air filter for Roomster. It has a white soft sleeve over the paper filter. Does this white sleeve have to be removed or does it remain covering the paper element?

The white glass fibre matted sleeve is part of the filter. Leave it on.

Thanks xman, I will do. It appears rather dense for air to pass through it.

I was surprised by the good condition of the old one. It had done 20k but the white sleeve was only slightly grey and was dry and no smelling of oil or petrol. Lifting  the cover of the airbox to gain entry to the filter the pipe which pushed onto the pcv did become free to my horror. I thought I had broken the valve but the pipe pushed back on. That might be a tip to disconnect the pipe from the valve next time to avoid breaking the corrugated end which pushes into the manifold. The pipe was clear with only a smear of clean oil in the end of the pipe. 

Its a heavy-duty filter if its got the sponge bit on the end. They have two listings for this filter. Standard/heavy-duty. I use the latter for my diesel car