A spokeswoman for the Maritime and Coastguard Agency said: “Our surveyors have carried out a full inspection of the European Causeway and are satisfied that it is safe to sail again.
“A ‘condition of class’ has been issued by the Flag State’s Classification Society which requires the shaft generator not to be used for provision of main power.
“The shaft generator uses the propeller shaft to generate electricity and does not affect the sailing of the ship.
“In the meantime, the European Causeway can rely on other generators for its electricity use.
“There are no further inspections of P&O Ferries at the moment but we will reinspect when requested by P&O Ferries.”
The European Causeway, with more than 100 passengers on board on the service to Cairnryan, Wigtownshire. was escorted back to Larne by three lifeboats.