Confidence: It's likely to be this, but I can't be certain.
Notes: The colour of the cap, the very thin and weak veil remnants on the cap, and the evidently fugaceous ring all suggest it is A. gemmata rather than A. citrina. The left-hand photograph has a very slight suggestion that the cap margin will become striate with age, but it is not clear enough to of use in identification. Best would be confirmation that it has inamyloid spores. A. gemmata grows with a number of tree species and at a Scottish site we have known for many years it is mycorrhizal with Rock-rose (Helianthemum).