Naiive new landlord made big mistake - how to fix - no tenant details

Tenancy Types and Management

Hi I purchased my 1BR flat at auction, with the intention of ,moving in myself initially.  The tenant showed me around, offered me tea, and was generally very helpful.  I purchased with him in it, and just took over the AST of the seller.  However, the AST did not include any details of the tenant, such as date of birth, source of income, the usual checks.  He just told me he was a pensioner on housing benefits

Things have now gone pear-shaped.  I need to engage a Managing Agent to keep the tenant at arms length and establish a professional management structure.  The Managing Agent won't take on the tenancy without these personal details from the tenant, due to their rent-insurance policy.  Is there any way around this, or how can I get the tenant to now supply these personal details? Thanks