A vintage Marks and Spencer black teddy or camiknicker, in the style of 1930s 'step-ins'.  Adjustable straps.  Flares at the waist, in the style of French knickers.  Gusset fastens with 6 press-studs. 100% polyester, with floral pattern.  Dates from late 1980s or early 1990s.

Size 12, but would guess that this equates to size 10 nowadays.  Please let me know if you would like more information.

The fabric has stretched slightly where the straps meet the body at the back - could easily be repaired or strengthened with needle and thread.