Confidence: I'm as sure as I can be.
Notes: I am reasonably sure this is a colour form of L. lubrica. There is a green species, Leotia chlorocephala, rarely reported in Britain, but in my understanding that is a rather different shape and lacks any yellow. [N.B. in Fungi of Switzerland, "Leotia chlorocephala" is water soaked Microglossum viride.]