This is a slime mould called Trichia decipiens. It's a fairly common species which grows on rotten logs in wet woodland. The fabulous tangerine coloured fruiting bodies are the spore producing sporophytes, which occur on little stalks. They are very small (about 1mm in diameter and 3mm high), but they normally occur in clusters like this, which makes them more visible. You usually find them when you're looking for something else! Slime moulds are often studied by mycologists (people who study fungi) but, in fact, they are probably more closely related to the microscopic animals called protozoa (e.g. Amoeba and its allies). There are hundreds of them in Britain, many are exquisite and the majority of them grow on decaying wood and plant material in woodlands.
The specimen shown here was found on a rotting log in the Clydach Valley near Bryncoch.