I agree with @Fairygirl, both the Hairy Willowherb and the type known as Fireweed are perennials spreading by rhizomes as well as by seed, and overwinter in most parts of the UK.
What size is it @*Astrantia* ? That can help with ideas if we have the scale. It looks a bit like ox eye daisy foliage too, but there are lots of plants that are similar.
Sorry but leaves wrong for leucanthemum vulgare..common name ox eye daisy.
I've had this plant appear in an old pot of compost, I assumed it was willow herb but it looks different to the willow herbs that appear in other areas of my garden..
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Epilobium hirsutum
https://www.wildlifetrusts.org/wildlife-explorer/wildflowers/great-willowherb
known around here as ‘Codlins and Cream’ as the flower is the colour of a dish of baked Codling apples and cream.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
being I pulled them up! they had small roots not deep and I know I didn’t plant them!