Well there is the ever changing name from the Forest of Dean ....... and Miss C used to be a copper.
I believe that an arrest on suspicion is good enough to go to court and hold onto him as they only have to prove "reasonable grounds to suspect that the accused has committed a murder". That would require that they are able to demonstrate that he was seen to drive off with the missing child or that they have found DNA to show she had been in his car and not seen since.
PACE (Police and Criminal Evidence Acts) does make provision for a person to be arrested and charged if the arresting officer has reason to believe that the accused has committed or may be about to commit a criminal offence .... Or at least it did when I attended the lectures on it, but that was 15 years ago and the law is constantly changing