Not a difficult puzzle. Some familiar clues (14ac, 19ac, 21dn) provide the starters. First I finished the lower half; in the top half, the left quadrant was the last to be completed.
Across
1 HEDGEROW – H (edger)ow – Not one with green fingers, I came to know of ‘edger’ only today. ‘How’ is given gratis; we don’t realise this until later.
5 FIDDLE – Fi(DD)le – I was initially thinking of ‘diddle’.
12 ERODE – (-h)er ode – There is a town in Tamil Nadu whose name we spell this way.
13 IMPLEMENT – Imp(-a)lement
16 MISSION – (-O)mission
23 ADORATION – Ad oration – Bill at other times could give AC (from account, a/c).
25 OLIVE – O live (‘live’ as in ‘live wire’)
27 CRACKERS – two definitions
29 REPRISAL – Re(pr. is)al – concrete (‘real’) as in ‘concrete evidence’.
Down
1 HAMLET – Two definitions – ‘Play’ is a verb in surface reading but as definition for required word, it is a noun.
2 DOCTORATE – Doc (dwarf) to rate (deserve)
3 ELATE – (-R)elate – ‘associate’ as a verb gives ‘relate’ – I would prefer “… when Romeo is gone”.
4 OPINION – O pinion – ‘shackle’ is a welcome change from the usual ‘wing’.
8 EVENTING – E venting (‘giving voice’)
17 ITCHINESS – It(chin)ess*
18 ASSASSIN – As (when) SAS (crack troops) -sin (go astray) – SAS: Special Air Service. Nice to see two fools left alone.
20 LAID – rev. of ‘dial’, v. ‘to ring or call someone’.