Puzzletome Crossword Puzzles

March 2020 Monthly Crossword
Badmouthing

Seven clues are missing the definition and the answer. Ten otherwise normal down clues contain an extra letter in the wordplay. In clue order, these letters give the theme.
Grid
Across
6 Single slice on cafe floor (5)
7 Naive rise in remarked returns (8)
10 Music sung first by singer back down under? (7)
11 An article is a bit of trouble without belief (7)
12 National Insurance (small contribution) to serial killer (7)
13 Carbon left in ideal facade (7)
14 Primate catching first plane by airport fighting fit (11)
19Have another union for railway and rearm workers inside (7)
21 Turn X49 inserting single implement (7)
23 Empty small hoover, we heard, around mid January (7)
25He'll dowse anger with Millwall's top supporter circling (7)
26 University of Rome playing around snippet from string quartet (8)
27Runners up in strenuous pinata playoffs admit regret (5)
Down
1 Ecstasy dope, Uriah Heap? (8)
2 Acting edgier with Redford second rate (6)
3 Warning man toy radio is broken (10)
4 Spiritualist upset in drama class (4)
5 Fair and ill dispositions of children (6)
6 Salsa dancing around Hawaii trailer trash (6)
8 Animal concealed in a nice building (7)
9 Energy in street commercial taking place (5)
13 Cross after apex of chateau has merciful release (10)
15 Room to look angry after a bit (7)
16 Group seem upset about north bitterness without hint of involvement (8)
17Extracts give Romeo's antipathy vis-a-vis Escalus (5)
18 Drop police line up - catch leading gangster (6)
20 Pairs of Maori cricketers onrushing (6)
22They're wrong to perform in rear wheel (6)
24 Quickly - that way, boy (4)