Section 5 of FEPA requires a licence for the deposit of substances or articles in the sea or under the seabed and for the incineration of substances or articles at sea. However exemptions have been made for discharge of cooling water from a vessel or installation under the Deposits in the Sea (Exemptions) Order 1985.
No consent/exemption is required. The Deposits in the Sea (Exemption) Order 1985 provides a general exemption for the overboard discharge of black, grey and cooling water. Other legislation would control or prohibit discharge if it contained oil or chemicals.