Four unclued lights of a kind, one of two words with an apostrophe, include the theme word. The remaining unclued lights (one as a pair), all but the literary solution at 41 Across verifiable in Brewer, can be linked with this theme word. Elsewhere, ignore one accent.

Across

1 Psephological survey that’s on the way out (8, two words)
5 Film involved spy chief getting Oscar (6)
12 Socialist sympathisers at peak on Greek isle (6)
16 Dockland structure seems blackish (5)
17 Swarmed like fish and cruised into shallower water (7)
18 Curious way to row (7)
20 Deliver one rebuke after start of lesson (8)
28 Couple...