Why would someone who was never charged and has never been publicly named seek prosecution unless it's to intimidate and bully the witness?
If he has/had a well paid job which is dependent on DBS, then he might have felt he had no choice.
The police have concluded that a crime was committed and have closed the case.
So he will have an allegation of rape on his record, and therefore on his DBS disclosures, for ever. DBS covers all 'caring' professions and anything to do with children (including fostering and adoption).
Now, with the exception of the specific barring lists (which I doubt he'd be on), DBS does not specify who can or cannot do what job. Instead the disclosure lists all convictions, cautions, reprimands, warnings and (for serious offences) allegations and it is the employer's responsibility to perform a risk assessment in each case. However, employers are now so risk averse that anything other than a perfectly clean DBS disclosure is likely to be a complete career stopper - why would you take the risk on somebody with a rape allegation on their record? And DBS has to be re-checked at least every 2 years.
So if he is, say a senior doctor, counsellor, social worker or teacher, I can well see why he would spend £200 grand to try to clear his name, as an alternative to spending the rest of his life working in Lidl.
Alternatively of course, he could just be a very rich evil bastard.
I heard the father on the radio, and it was heartbreaking. His candid account revealed that the case was not quite as black and white as others have assumed, but I still don't understand what the CPS thought they were doing. Everybody knew she had current mental health issues - even if, for a moment, we consider the worst possible case and assume that, even though she absolutely genuinely believed it herself, her claim was not true, why on earth would the CPS even think of prosecution? Mentally ill people make all sorts of claims all the time, but the CPS doesn't prosecute them.
It's all just so very very tragic in every respect.