Sounds like a cable issues. Could be the cable needs oiling or it is starting to fray. Remove the cable from the clutch lever side and check around the end for signs of frayng. If all checks out remove the cable from the clutch end and see if it pulls cleanly through by hand (it should be very easy to pull/push) if not put a bit of tape around the clutch lever end of the cable to create a bit of a funnel and fill it with WD40 and pull/push the cable, repeat until the WD40 comes out the other end. Grease the pivot at the lever side before you put it all back together..
Well that was embaressing... I am still waiting for the new cable to arrive but as I had a bit of time today to do a few jobs on the bike so I thought, why not lube the clutch cable just to take the strain off it until the new one arrives. Guess I wont be needing the new cable after all.