UK Landlord Forum / Life

A estate agent found for me the tenants and they did the checks with them.
The tenants are about to leave (I hope so) because they don't pay since 3 months ago and for the next tenancy I don't want to use a estate agent.
I asked the agency about the passports from the tenants because I think I'll go legal against them but the the agency don't want to give me them because they say they are not allow. Is this right? If I ask the tenants for the passports they're not going to give them.
Many thanks in advance.