(7) Without prejudice to subsection (5), and whether or not a prosecution has been taken under this section, where a person on whom a notice is served under subsection (4) fails to carry out the required remedial action within the period specified in that notice or to complete any works specified in an injunction of the High Court under subsection (5), the water services authority which issued the notice, or a person authorised on its behalf, may enter the relevant land, carry out the remedial action or complete the specified works, and recover the cost from the person who fails to comply with the notice or injunction.