My immediate reaction was 'Ragwort', looking at butterweed I wonder if they are the same thing, different names, there are various types.
Oxford Ragwort, the common one over here, was brought back from the Himalayas and grew in a botanical garden in Oxford. It likes shale and pebbles, escaped to a ruin next door, and for some time was confined to there. Then they built the railway and it found embankments the perfect environment and spread all over Britain. Regarded as a 'pernicious weed' because it is poisonous to cattle and horses.