Powdery mildew occurs in hot dry spells, mildew in damp spells, not uncommon, particularly where planting is crowded. Either spray with a suitable fungicide, or use a 1 in 10 solution of milk in a spray bottle and spray with that.

Also worth noting that overcrowded planting and not enough watering will encourage it.

Thanks so much for the advice.
I guess they are overcrowded, so may have to get rid of something, sadly.
I will start spraying anway.

When you move things about just replant the moved ones, don't sling them out - that's awful, they're much too dear to get rid.