update - the pollen filter is indeed at the back of the passenger footwell as JohnH describes - take off the centre console panel at the bottom of the centre console in the footwell, there are 2 clips that you wedge open and pull out. Next take out the liner under the glove box, there are 2 push-on/pull-off black covers over yellow stalks. Next take off the fuse-box, twist the clip 90degrees and lower the fusebox and then pull it off the 2 hinges once lowered, and push it to the left as far as poss. Undo 3x 7mm screws/bolts with a small socket wrench. Pull out old crappy dirty black filter - you can concertina it to get it out of the space. Similarly putting the new one in - it can be concertina'd to fit back in. Pic here of where the cover is - its in the centre of the pic with the regular rectangular cut-outs. Took me about 45mins to get this done once I realised what on earth you're supposed to do.