Dust chicken pieces in flour. Heat oil in a flameproof casserole dish on high. Saute chicken, in batches, 2 minutes each side, until browned; remove and set aside.
Reduce heat to medium. Add onion and garlic to pan; saute 3 minutes, until soft. Return chicken thighs to pan; add wine. Bring to boil. Simmer 2 minutes, until wine almost evaporates.
Add passata and 1 cup water. Cover; simmer 5 minutes. Add drumsticks; cook, covered, a further 5 minutes. Add remaining chicken and anchovies; simmer, covered, 15 minutes, until cooked through. Stir through shredded basil and scatter over olives.