I too have never heard of a situation like this. I would first draft a formal letter to him citing that unless he complies with your request that you will be forced to pursue two courses of action.
The first will be a civil claim in the County court for the records you are owed under the principles of equity. "Equity" is a form of common law which allows the court to use their discretion to impose natural justice in line with the law. You should intimate that you will be pursuing him for the records, your legal costs plus interest.
Your second cause of action will be to pursue a criminal grievance by filing a complaint with the police that you have a suspicion of fraud.
You should remind him that you have spoken with a solicitor and that failure to comply this time could result in penal costs plus a criminal investigation. Give him a deadline of 14 or 21 days to comply.
Should he fail to comply with this then unfortunately you will have no option but to follow through on the above. In respect of the law suit you could look into two options to keep the costs down
1. McKenzie Friends - These are legally trained individuals (usually paralegals or law students) who will assist you with your case for a low fee.
2. Pro bono - Look into pro bono clinics in your area that you can visit. Pro bono solicitors do some work for free. They may be able to take your case on for free if they feel it is suitable.
I would also contact the police and make a complaint if you genuinely suspect fraud.
I hope this helps.