I've just replaced them. Not that they were causing problems because they are super wiper blades. I just decided to make it a regular maintenance task.
http://www.ebay.co.uk/itm/Rover-75-1999-ON-FLAT-AERO-WIPER-BLADES-22-22-/310350887994?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item48425abc3a
At that price, it would be churlish not to