The Pride of Kent, a P&O ferry, has failed its reinspection by authorities.
The Maritime and Coastguard Agency (MCA) said: “The Pride of Kent remains under detention after failing to pass its reinspection today. We will reinspect when requested to do so by P&O Ferries.
“There are no further inspections of P&O Ferries at the moment but we will inspect when requested by the company.”
The Pride of Kent was detained at Dover after failing safety checks in March.
P&O Ferries used to have four ferries operating on the Dover-Calais route – but only one has been cleared to resume passenger services since the company sacked almost 800 seafarers in March to replace them with cheaper agency workers.
Drive-on passengers and tourists were able to use the service for the first time in almost six weeks today by boarding the Spirit of Britain.
The ship has been crossing the English Channel for the last several days, carrying freight-only traffic.
The ferry operator said it is operating on a reduced timetable on Tuesday and is set to resume a normal schedule on Wednesday.
The company suspended its services in March when it announced the redundancies of its staff, which had been made without consultation.
P&O Ferries was then told each vessel in its fleet must be deemed safe to operate because of the widespread change in crew.
Upon inspection, the MCA found a number of safety failings that have dogged the ferry operator for weeks.