UK Landlord Forum / Life

I have a three bed house terrace let to a family and managed by a small agency. Whilst being good long term tenants they are several hundred pounds in arrears with no sign of paying this off. The managing company are unable to re-new the tenancy agreement as the tenant does not wish to, the tenants have only just gone on to standing order, wont even consider paying arrears off and enjoy holding us all to ransome with varying rental payment dates around the agreed due date. We will see how the new standing order goes. 

Do I serve notice? They have asked for a replacement front door, new carpets, tiling in the bathroom etc but we are no further on with arrears payments. They are now paying the correct rent amount but won't even pay the smallest amount of arrears. Do I look after them or go in heavy? The management company are ok elsewhere but can't make any progress with these tenants. 

Any help appreciated.