Is it water spots?

Not rust, patches are too big. Rust is little raised orange pustules. This looks like water splash in the hot sun, possibly?

I put a blog on recently asking if my Georgia peach had rust, the answer was yes but it didn't look like this Gee.

It looks as if the back surface of the leaf has been eaten away in parts, just leaving the front face.

Could be Leaf Miners. You get then also on perpetual spinach and beetroot.

Thank you all, great relief that it's not rust. Sorry, you wasn't as lucky, Annella. I haven't watered my garden, apart from bowls of (reasonably clean) washing up water straight onto the soil. These Blackberry James are in the same bed as some green/yellow heucheras which are entirely unaffected.

I have just been out and peered at a few more badly affected leaves and it does seem as if the damage is being caused on the back, just as you say Bulbaholic. I can't see anything creeping or crawling. I do have slugs so will venture out with a torch tonight to see if I can spot any pests. Then I wondered about cutting off all the affected foliage to see if they return to their former glory?

Avgood Idea as long as its not too many I think Gee, they do go a bit scruffy round the edges it seems

Did you ever find out what the problem was? My Georgia peach heuchera looked the same way! Just planted this spring :-(. Please let me know if you have any success or found anything that helps. I am worried mine may be getting too much sun.

Goodness, that's such a long time ago I really can't remember! I think i still have a couple of these plants in the garden which have been periodically divided and replanted so it was definitely nothing terminal. Hope your Georgia Peach recovers too.