I think I must have been starving my lupins. First the leaves started to turn yellow and when the flowers opened they were looking very pale and smaller than usual.
The flower above is the colour they usually are and below shows a rather sick looking one and the yellow leaves. These are both on the same plant.
I think I should probably feed them more often so out came the miracle grow and now hoping things will improve. Maybe a bit too late for the two affected plants but I have treated all of them.