Looks like Feverfew
Thank you for posting - I was hoping someone might know what they were!
I think you're spot on there - the leaves seem to match, and the description says they spread abundantly if left... which they had been. (The extra land I bought was my neighbour's garden, and it had been overgrown for a couple of decades).
Maybe a variety of Hosta
These are interesting - I remember my mum calling them lilies, or so I thought, but on reflection she was probably talking about the adjacent pond (which did have lilies back in the day - not any more).
The flowers for Hosta look different, so I turned to "AI" - turns out there are a number of services, including on the RHS website, where you upload a photo and it tells you what it is. Both the RHS and a different service came up with:https://en.wikipedia.org/wiki/Bergenia_crassifolia
I'll have a look tomorrow and see whether those flowers are on a red stalk. If they are - I think that solves that mystery!