I too think it’s a form of mache or lambs lettuce, If it’s the same as I have it tastes lovely, but pick before it flowers or the leaves get elongated and a bit bitter… but to be honest it does spread quickly so if you don’t like it pull it up quickly, it does not have deep roots and is easy to remove.
Marne la vallée, basically just outside Paris 🇫🇷, but definitely Scottish at heart.
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Cannot see that in mystery plant.
We need a clear pic.
https://www.google.com/search?q=lobularia+maritima&client=firefox-b-d&sxsrf=APq-WBt4QIFZKnE4vMBs5e_jWpTrktcXyA:1650704869041&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjIp-Tq6qn3AhVxQ0EAHT76BvcQ_AUoAXoECAMQAw&biw=1280&bih=595&dpr=1.5