1: Dirty work outside of school (5)
4: Defects called for a metal cache underfoot (5,4)
9: 23% of Scandinavians backing leaders (3)
10: Object to professional examination (7)
11: Now Elton heard California's big one (3)
12: Clothilda is carrying a parcel (3)
13: Don't encourage satellite pace to slacken. (11)
14: Travel - pioneering art form (13)
17: Working on mental topic? (13)
20: Invention to trick four into a stupor (11)
21: What this puzzle is (3)
22: Three kernels of copper-yellow grain (3)
23: Outfit wins Tet Offensive (7)
26: Get into the archeology scene. (3)
27: Avoids seeds, pits, nuts (9)
28: Report build-up on cable tower (5)