Unclued lights have something in common, nine of two words, five pairs, and one singleton.

       Across

10  Always hard to keep a maid (4)

13  Only covering one’s losing bid (6)

15  Put down women’s medieval instrument (5)

16  Follow the game secretly from chimney (5)

21  Indian wasting minutes in queue (4)

22  In recess, they are on the phone to reporters (4)

24  Yank pokes right inside basket (4)

25  Sort of breakfast originally eaten day after day (5)

27  Observe baseball player striking woman (3-7)

28  Not altogether keen about lecturer’s lectern (5)

37  Helps receive salmon, about a stone (2-5)

38  Alastair’s extended half of speech (4)

40  Fish,...