Armillaria mellea, Honey Fungus. One of our commonest fungi, and the scourge of gardeners. However, the Honey Fungus is much-maligned, as it is doing a great job decomposing and recycling all our dead wood, and returning the nutrients to the soil. Also you can get your own back and eat it! (It should be well-cooked and does disagree with some people) The fruit bodies appear in large clumps and there is always dead wood nearby, although it could be on buried roots. The cap is a honey-colour when young. At this stage it often appears dusted with golden particles, and as the fungus ages, these turn into dark brown spots on the cap. Cap diameter is 5-12cm, stipe 5-15cm with an obvious white ring, often edged with bright yellow. Once in your garden it is almost impossible to get rid of it. It attacks mainly ornamental non-natives, most native species being resistant. Here is a short, non-comprehensive list for those of you with problems.
Susceptible - lilac, privet, flowering cherries, non-native willows, walnut, cedars, cypresses, Monkey Puzzle, Wellingtonia
Resistant - Box, elder, yew, hornbeam, beech, ash, oaks, juniper, larch, whitebeam, bamboo, Grand and Noble fir.