Fumaria muralis ssp. boraei
Just for comparison with the White Ramping-fumitory (Fumaria capreolata) in the post below, this is Common Ramping-fumitory (Fumaria muralis). Distinctive features include the rose-pink colour of the flowers which have black tips on the the upper and lower petals. The flowers are also slightly smaller than those of White Ramping-fumitory and there are less flowers in the inflorescence (usually about 15). You are more likely to confuse this species with Tall Ramping-fumitory (Fumaria bastardii) or Purple Ramping-fumitory (Fumaria purpurea), both of which occur in Gower. The upper petal of Tall Ramping-fumitory doesn't usually have a dark tip, while the calyx segments (sepals) of Purple Ramping-fumitory are very large, more than half the length of the flower. If you enlarge the photo, you should be able to see the calyx segments easily - i.e. the small appendages with jagged edges on the sides of the flowers. The size and shape of the calyx segments and the nature of the toothed edges are important features that characterise fumitories.
Common Ramping-fumitory is a very common species of waste ground all over Britain. The specimen in the photograph was growing near Margam in a diverse, weedy community that included some fine specimens of Bargeman's Cabbage (Brassica rapa ssp. sylvestris).
Brassica rapa ssp sylvestris
Bargeman's Cabbage is very similar to Oil-seed Rape (Brassica napus ssp.oleifera) and I always assumed that the large, showy, yellow-flowered crucifers growing along the hard shoulder of the M4 between Briton Ferry and Margam were Oil-seed Rape. It's difficult to make an accurate identification at 50 (or 70) mph! Having seen these plants, just off the motorway, I'm beginning to think that the plants along the M4 are mostly (if not all) Bargeman's Cabbage. Please comment if you have any opinions on this matter.
Bargeman's Cabbage differs from Oil-seed Rape mostly in the features of its flowers and inflorescence. The flowers of Bargeman's Cabbage are smaller and a much richer yellow than those of Oil-seed Rape. The flower clusters in the terminal inflorescence of Bargeman's Cabbage overtop the buds, so the buds are not visible (enlarge photo to check this out). With Oil-seed Rape the flower buds are usually much more visible and often stand clearly above the open flowers.