What is a blackbird with white underbelly and orange beak seen foraging on the welsh coastline?

The bird you are describing is likely the Eurasian Oystercatcher (Haematopus ostralegus). This coastal bird has a striking black body, a white underbelly, and a distinctive orange beak, which it uses to forage for shellfish and other invertebrates along the shoreline. Oystercatchers are commonly found on the Welsh coastline and are known for their loud, piping calls.