The boss of P&O Ferries has insisted he will not reverse the decision to sack nearly 800 seafarers despite being given “one further opportunity” by Transport Secretary Grant Shapps.

Chief executive Peter Hebblethwaite wrote to the Cabinet minister claiming his request “ignores the situation’s fundamental and factual realities”.

Re-employing the sacked workers on their previous wages would “deliberately cause the company’s collapse, resulting in the irretrievable loss of an additional 2,200 jobs”, the letter stated.

“I cannot imagine that you would wish to compel an employer to bring about its own downfall, affecting not hundreds but thousands of families.”

When P&O Ferries announced its decision to replace its crews with cheaper agency workers, it stated that the business needed to cut costs to survive as it was losing £100 million a year.

The Prime Minister’s official spokesman said “commercial challenges” do not provide an excuse to “subvert the law or treat employees in the way that we have seen from this company”.

The Maritime and Coastguard Agency (MCA) said the detention of a second vessel belonging to P&O Ferries was due to failures with emergency equipment, crew training and documentation.

Pride of Kent was held in Dover on Monday following the detention of European Causeway in Larne, Northern Ireland on Friday.

Mr Hebblethwaite was responding to a letter from Mr Shapps which stated that P&O Ferries had “one further opportunity to reverse this decision by immediately offering all 800 workers their jobs back”.

The ferry firm boss also rejected the minister’s request to delay the deadline of Thursday for sacked workers to accept redundancy offers, as more than 765 of the 786 affected people have “taken steps to accept the settlement offer”.

He wrote: “These are legally binding agreements, and crew members who have entered them will rightly expect us to comply with their terms.”

The chief executive insisted he will continue in his role despite Mr Shapps describing his position as “untenable”.

I am compelled to discharge my duties for this historical company, saving the jobs of the 2,200 dedicated employees who continue working for P&O Ferries and providing for the effective operation of the trade routes upon which this country depends

Mr Hebblethwaite wrote: “I am fully cognisant of the reputational cost to the P&O Ferries brand and me personally.

“That notwithstanding, I am compelled to discharge my duties for this historical company, saving the jobs of the 2,200 dedicated employees who continue working for P&O Ferries and providing for the effective operation of the trade routes upon which this country depends.”

Mr Shapps plans to introduce a package of measures in response to the situation this week to ensure “seafarers are protected”.

On the detention of Pride of Kent, an MCA spokeswoman said: “The Pride of Kent has been detained due to failures on vessel documentation, crew familiarisation and training, and emergency equipment not functioning properly, indicating a failure of the implementation of a safety management system.

“We have advised P&O to invite us back once they have addressed the issues. We do not know yet when this will be.”

The MCA said it needs to inspect eight of the firm’s vessels before they can return to sea.