What's wrong with this Peony?

Looks like either weedkiller damage or virus (unless the discoloration on the leaves can be rubbed off) If its viral there's not much you can do except feed it up a bit and hope it gets better; bit like humans, really!

Thanks for that Bamboo - it probably is weedkiller damage as it is in an area where my other half Glysophates the path. A stern telling off is in order!!

This looks to me like localised iron deficiency better known as 'lime induced chlorosis'. There is a sprayable product named "Sequestrene" which should solve the problem and won't do any harm if it isn't.

Thanks for that Bigbumblebee - it's worth giving it a try.

Worth a try, but I'm sticking with my original opinion - the torsion and twisting of the leaves convinces me;-)