It's Chelidonium majus, a weedy member of the poppy plant that closely resembles Styllophorum diphyllum, a native wildflower that's also a member of the poppy family. Here's a page that tells about the two and how to differential between them. For many years I wondered why folks liked celandine poppy, but it's because I have the weedy Chelidonium majus, not the native, better behaved plant.

I agree Alison (though I haven't noticed any bees, I think the conditions lately have done terrible things to their numbers). I have just moved it (by propagating some more) away from my back door, where it has been a little too fragrant when I sit for my morning coffee. When it has finished flowering I will pull it out and I will need to find something else hardy, low, drought tolerant and attractive to take its place. The sunny parts of my garden are full of various succulents, geraniums, chilli, salvia, angelonia, shasta, osteopernum, chrysanthemums a few natives - all the tough old plants that can do the distance in this tricky climate with unpredicatable rainfall. I now just need to find something else this low, this dense, and with this many flowers that can cope in a harsh position. Always on the lookout... an addict!

I think it's pipsissewa AKA spotted wintergreen, Chimaphila maculata. It's a native woodland plant, so I am not sure that moving it to more sun will make it happier. I'd at least put back a mulch of pine needles. https://gobotany.newenglandwild.org/species/chimaphila/maculata/

Looks like Iresine herbstii, AKA beefsteak plant, chicken gizzard and bloodleaf.