Dapo Adegboyega has been accused of coercing a congregation member into obtaining a £100,000 loan for him at his previous church before joining SPAC Nation.
The suspect has since been bailed pending further enquiries.
A man has been arrested on suspicion of fraud offences and was questioned at a south London police station. He has since been released under investigation.
The Charity Commission says its inquiry into the church is ongoing.
The Metropolitan Police is understood to be actively looking at about 20 to 30 cases.
Scotland Yard has said it will not launch a criminal investigation into SPAC Nation - but one alleged victim says she has not even been contacted by detectives.
Ministers hear demands for SPAC Nation to be stripped of charitable status while it faces two probes.
Pastors are alleged to have held a sign-up day for Universal Credit at a SPAC Nation trap house and asked young churchgoers to hand over half of the payments
The key allegations against the London church, which has been investigated by HuffPost UK, BBC Panorama and others.
The Charity Commission said it has opened an inquiry into the church to probe financial and safeguarding concerns.