It is the responsibility of the owner/occupier of the property affected by a blocked or defective drain to clear or repair it.
Even though a drain can go outside the boundaries of the property it serves, such as under the road to the public sewer, this section still remains the responsibility of the owner/occupier.
If your property is insured it may be prudent to speak with your insurance company if you are experiencing problems with your private drain.
Council house drains are the responsibility of Wigan and Leigh Housing (external link).