Exit fee from agency

Other

My tenants came through the agency a couple of years ago, and I will now be directly dealing with them so I have to buy the tenant from the agency.  The cost is £360.  I haven't increased the rent since the tenants moved in and have offered to keep the rent the same this year too; however, I have requested them to pay the exit fee.  The tenant is happy to do that, however, he doesn't want the rent to increase What is the best way to go around this legally? He said he would pay the agency directly, however I believe that would not be the best way to do it.