Hi Johnny, good news on tomatoes!
Powdery mildew, soft and fluffy on top of leaves, looks worse than it is and mostly affects older leaves, not often the ones you might eat, but can be washed off to eat them. Yes there is a lot around, for example I have some on kale which was covered with mesh until Saturday and am not worried about it. It certainly won’t kill them, they are in full growth.
On the other hand, peas in late summer often suffer badly from it and hence my suggestion to sow peas in March to early May rather than June and July. It is a natural occurrence as the pea plants’ energies turn towards fruiting in autumn. Similarly with courgettes and squashes so don’t worry if you see it on their leaves, the older ones mainly.