I noticed on the Citroen UK web site they now offer air deflectors for the front window on the C4 Picasso at about £50 when you buy a new car.
So, I rang the main dealer at Kings Lynn (Duff Morgan) and told them the price (so there was no confusion
, they ordered them and they are now fitted 
The total cost was £50.82 including VAT.
If anyone is interested the part numbers are:
C4 Picasso - B785
C4 Grand Picasso B787
I bought some very good after market ones for my Xantia and they took a few weeks before the anti-pinch settled down as I suppose the window rubbers have hardened; the paperwork with the C4 Picasso ones says wait 12 hours, I waited 24 and the windows shut as they should.
Very happy
Maurice