The coastguard has confirmed it is carrying out a safety inspection on one of P&O's suspended ships.
Inspectors have embarked the vessel, currently berthed at Dover port, at the ferry firm's request in order to see if it can be cleared for sail.
Safety inspections are necessary after P&O sacked nearly 800 of its workforce on March 17 in a shock move with no prior consultation or warning.
It replaced the experienced seafarers with agency staff, being paid a lower wage.
The firm said it had no choice but to lay off staff and replace them in order to save it from going under in a move that has been condemned by the government, trade unions and public.
No P&O ships have sailed from Dover since the mass firing, which sparked protests and calls for the company to be boycotted.
The Maritime and Coastguard Agency (MCA) have already carried out an inspection of the Pride of Kent, which also sails the Dover to Calais route, which it failed.
The ship remains under detention.
Today, the agency says it is now carrying out an inspection of the Spirit of Britain.
A spokesman for the Maritime and Coastguard Agency said: “An inspection is taking place at P&O Ferries request on the Spirit of Britain.
"All inspections have to satisfy the Maritime and Coastguard Agency that the ferries fulfil the requirement of the Port State Control regime and are safe to put to sea.
"There are no further inspections of P&O Ferries at the moment but we will reinspect at the appropriate time."
The Pride of Hull, which runs the Hull to Rotterdam route, and European Causeway, Larne to Cairnryan, have been inspected and cleared to sail.
Four other ferries are yet to be inspected, while the Pride of Kent will need to be reinspected before it can sail.
It comes as P&O Ferries said it was hoping to resume its serves from Dover this week.
In a statement released last Wednesday, bosses at the firm said it would be preparing to 'resume services across a number of vital routes'.
But yesterday, the firm confirmed that journeys on any of their vessels to France have been cancelled until Good Friday.
Formal criminal and civil investigations have been launched following the mass sacking, with the Insolvency Service looking into the actions of the ferry firm and whether it broke the law.
The suspended services have had a knock-on effect on Kent's roads, with delays at the port leading to Operation Brock being put into action and other road closures.