I have a plantWhich I think is Darmera peltata

Might be Nicandra physalodes, also called the shoo fly plant

https://www.rhs.org.uk/Plants/52667/Nicandra-physalodes/Details

Definitely not Darmera peltata; that has individual leaves with a central stalk, like umbrellas. ID not coming to mind at the moment, hope someone else knows!

My Shoo fly have all died back with the frost and been cut down but if Bamboo is right, and the leaves do look the same, mine had tiny, tiny black "spots" on the leaves. A good tell tale when they're first coming up.

The flowers are the easiest to ID it by... there's an image of those in the link, but you're right, Thorneyside, in many parts of the country, Nicandra will have shrivelled back with the frost, though here, only this last week... my pelargoniums are still in full throttle, covered in flowers outdoors on my windowsill.

I've never seen such a big specimen of the Shoo- fly plant, though the smaller leaves certainly look like it. A fost will soon put paid to it I think.