My god there's a lot of presumption without any FACTS on this thread. !!
It's actually very simple OP. If he is unemployed then he simply needs to complete a c100 of the HMCTS website. Fill it in. Along with the EX160 form to be exempt from paying the court fee of £215. (Proof of low/no income - bank statement) or benefit proof.
Fill in both forms. Photocopy 3 times and take to the court.
If he is a dangerous , wife / child abuser then he will only get indirect or supervised contact OR none at all. If she is an evil bitch keeping her son from a relationship with his father then the judge will make an order based on the EVIDENCE and FACTS ! A report will be made to assess any allegations against your DP made by CAFCASS who will make a recommendation to the judge about the most appropriate way forward.
The mother doesn't get to make this choice.
If he is named on the birth cert or was married to the mother then this is all he needs to do. IF he has nothing to hide and is as innocent as you say then there is no reason for him not to do this right now !! If he is as desperate to see his son as you say. It will cost him nothing.
If he isn't named he has to first apply for Parental responsibility. An equally simple process. Same fee exemption.
If he doesn't PROACTIVELY do this then I would also believe he has something to hide but as my DH was in exactly your position I know that there are evil and vindictive women out there - and I am not prepared to jump to hysterical conclusions based on this limited background.
Tell him to get form filling. !
The court is very used to these sort of problems. We had his children returned within 6 Weeks.
No excuse for him not to crack on.
I would also get on to the legal board and ask these questions of the brilliant family lawyers who give their time to answer any questions. Their advice will be accurate and not filled with the assumption that every non resident father is a bad'un.
Just bear in mind that if he does nothing. Then he probably has more too hide. Until that point .. get on with it.