UK Landlord Forum / Life

I read with interest a recent blog regards late payment fees charged to tenants.
The letting agent that we employ to manage our property has a late payment charge of £75 written into their agreement. One of our tenants has left the property before the end of their tenancy. Unbeknownst to us he was late with a rent payment which incurred a late payment fee. When we recovered the deposit we found that the late payment fee has been taken from this, essentially charging us for our tenant's late payment.
Can they do this legally and do we have any redress in this matter?