It's Helleborus foetidus, a good plant for a shady border in early spring. Its flowers are little bunches of green cups and I find them quite pretty. I always have one or two that have self seeded here, so I'm never without, but they are never enough to be a nuisance. Though they like a limy soil, given the choice, so do tend to appear in the cracks between the paving!
Agree with buttercupdays. We have many varieties of hellebores and they flower at different times. This particular one does try to seed all over so we cut back the flower heads before all of them seed to prevent them taking over an area. We always leave some seedlings to mature for next year.
Do take care with the sap from the stems as they are an irritant.
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