SOLUTION to Chris Leyland No. 17:

Across - 5 Garland, 9 Leonine, 10 Rainbow, 11 Olive, 12 Elemental, 13 Dunce’s cap, 15 Carer, 16 Amass, 18 Scarecrow, 21 Somewhere, 24 Kendo, 25/1 Over the counter, 26 Anagram, 27 Ditches, 28 Therein. Down - 1 Colloid, 2 Utopian, 3 Triteness, 4 Reeve, 5 Garden pea, 6 Raise, 7 Arbiter, 8 Dawdler, 14 Casteless, 15 Checkmate, 16 Abscond, 17 Armrest, 19 Run free, 20 Woodman, 22 Witch, 23 Exact.