Certified Fraud Examiner.
Compared to under- or post-graduate University courses, it is ridiculously cheap to train but the ACFE qualification increases earning potential compared to fraud investigators; training and work can be intensive and stressful, but I thrived on it.
www.acfe.com/
www.acfeuk.co.uk/
I retrained as a Certified Fraud Examiner at 45. Its a great career change step because at his age he has far more life experience than a recent graduate, which is more than useful!!
Post-certification he could work anywhere in the world as it is a world wide recognised qualification.
Once qualified there are many sectors to chose from, including insurance fraud, civil servant (DWP, HMRC), NHS, police, accounting fraud, specialising in employee fraud is lucrative and very interesting and is the route I chose. The big well known companies from all sectors take on "undercover operatives"; ideal for those with no dependents, as operative examiners may have to travel further or more frequently, unless you're in London).
I took additional training in forensic linguistics (I love this aspect of the work), cognitive linguistics and forensic psychology. All these 3
are also good career changes independent of each other, or as I did, qualify with 1 first, then add on the parts that interest you most.
Message me if you have any questions. I finished work early due to ill health and always said I wouldn't retire as I love it so much.