Is it a weed, not a calendula?
Calendula leaves are broader and the flowers quite different. Your plant is possibly Valerianella species, otherwise known as Corn Salad or Mache. Cultivated varieties generally have smooth leaves, this one has hairy leaves. There is a species V. eriocarpa which is hairy and has the dense, tiny flowers in your photo. Found in the south of the UK, native to the Mediterranean.