Thanks for your replies, but it turned out I was premature – I ran another load and noticed that the clouding washed off, so obviously not lime scale. A quick check confirmed that the rinse aid selector had come loose and had rotated to its highest dosage. I put it back to normal (the lowest) and it seems to be working fine again.
One quick question – Would you need less or more rinse aid in hard water? The manual states that the amount of rinse aid needed is dependant on the harness of the water, but surely by the time the water has got into the machine it’s been through the water softener so is already soft?