Found mysteriously lying one each side of 'C sharp' (red hull, berth 19, behind clubhouse by roadway) beside the tie-downs: pair of Rooster black sailing gloves and what are presumably Lycra inserts. Now turns out they don't belong to my crew after all. Currently under C sharp cover at stern - owner please help yourself, or I will put them in the Members' Room for you next time I am at SYC.
I will have a look next time I am down, and will let you know about the inner. Or just help yourself from C sharp if you get there first! There were also what looked like two Lycra liners lying in the grass - may give further clue. Whoever it was must have put them on my cover for a moment and had their attention distracted.