If somebody drops charges (although this is a slight misnomer in English Law, as the CPS can still prosecute with or without the victims wishes) they will sign an official Police statement.
On that statement (all police statements) it will be pre-printed with the words
"This statement is true to the best of my knowledge and belief and I make it knowing that if it is tendered in evidence I shall be liable to prosecution if I have stated anything which is false or I do not believe to be true" (or something like that??)
Also on retraction statements they will sign words to the effect of
"I have made this statement of my own free will. I have not be coerced in to making it, and in doing so am in company with Police officers (and maybe solicitor) and no third party influence"
This will thus show he is a dodgy character.
He should be prosecuted, and he should receive not a single penny from any public purse.