Hi Ya, You are right JanG it is gallant soldier. I wonder if the seeds arrived with the potato tubers that did have soil on them and I and some other allotment holders have never seen it on our site before. My book on weeds where I identified it. It comes from South America and escaped from the botanic gardens in Kew. I wonder, having read my book if the other one is pearlwort. It looks similar. I will keep an eye on it and see. The gallant soldier apparently seeds freely and can be hard to get rid of. Good luck