Eight unclued entries comprise four pairs whose thematic ordering is provided by 3, 31, 37 and 41.

Across

1 Deft, dry in denial (5)

6 Bitter unit – British back in charge (7)

11 Criminal or liar with cult having three cells (10)

13 Distress furniture suitable for oils? (9)

15 Talks, say, regularly, inanely (4)

16 Extremities such as frogs’ legs do (7)

17 Thought mostly about minor inertia (7)

18 American-English custom (3)

19 To wit, PI hires corrupt eastern minister (10)

21 Put out cats, finally having enough (5)

23 Rigorous, way-to-the-right painter (5)

27...