I came across this fungus in the woods last week when we were clearing another patch of woodland in the reserve for replanting.
I think it is Chlorociboria aeruginascens, the turquoise elfcup but it could be the very closely related Chlorociboria aeruginosa, the green elfcup(!). It is a saprophytic fungus and these fruiting bodies are a few mm across.
The mycelium stains the wood blue as seen in these photos.
The blue-stained wood was used in marquetry in the 15th century in Italy and in the similar Tunbridge ware in England in the 18th and 19th centuries.