Thanks Clifford,
I haven't physically checked the filter but it was supposedly changed 3 months ago during a major service, I'm sure the garage can be trusted?
Had a go yesterday doing a 'perfume' check, not conclusive but my sense of smell maybe at fault, going to try again today using an aerosol spray, the one out of the loo and see if that works.
Fiddling with the controls with fan on max. opening and closing the air recirc did appear to change the air flow. Maybe it is working OPK?