Can I, and how do I, add these costs to tenants debts?

I am a landlord, I spend a disproportionate amount of time chasing tenants rents and debts.

Is it feasable for me to add these fees and interest on, and if it is at what point is it added.

So for example if a tenant leaves owing rent, then would costs be added from the date they vacate? In the case of an ongoing arrears situation (tenant still in situ) where an additional debt can mount on a monthly basis do I need to treat each monthly amount as a separate debt or work on it as a cumulative figure?

Thanks

As David says the legislation is only business to business. Private residential is a totally separate area of the law and I would strongly advise you to seek legal advice. The initial outlay will potentially safe you thousands in the long run ( even if the advise is simply to write it off).