Do we chase the Tenant or the Letting Agent??

This situation is very confusing and we are not sure if this is theft or simply a case of chasing by way of a CCJ.

We rented an apartment for many years with a local letting agent, with no problems at all.

Then last October a new tenant moved in, as the old one moved out.

The letting agent was employed to find a tenant only as he usually did and NOT to manage the property.

The letting agent gave us incorrect details for the tenant and we could not get hold of the new tenant.

The tenant kept paying cash to the letting agent who transferred it over to us each month after we had chased this up.
In May we finally received the correct details for the tenant from the letting agent after the letting agent’s brother looked on his personal phone instead of the tenant's file.

We spoke to the tenant and introduced ourselves and set up a standing order for the 9th of the month directly with the tenant. The letting agent knew this had happened.

The very next day the letting agent went round to the tenant's address and demanded the rent in cash off him, the tenant's girlfriend was scared and insisted the tenant handed it over. The tenant said to me he knew he shouldn't have given it to him as soon as he'd done it. Since then we have not been able to get this money from the letting agent, he has shouted at me on the phone and now ignores all emails and phone calls.

Is this a police matter for us or our tenant or do we chase our tenant for a missed rent or do we chase the letting agent through the court? He isn’t registered with the associations he used to be when we first started using him.