Tony Blair has said the government will be ready to help P&O workers who are to lose their jobs.
Two P&O ferries in Dover are due to be taken out of service
More than 800 posts are being axed among staff based in Dover as part of a plan by the firm to cut 1,200 jobs across the country.
The prime minister said he was "sorry" about the job losses but added those affected would be helped by the Department for Work and Pensions.
P&O is also withdrawing two ferry services from Dover.
Dover's Labour MP Gwyn Prosser raised the plight of the workers in the Commons.
During prime minister's questions, Mr Blair said: "We are sorry about the numbers of constituents that will lose their jobs.
"We stand ready to make sure the Department of Work and Pensions will give help to anybody who is made redundant."
The job losses were announced as part of a shake-up to revive the firm's faltering ferry business.
Two passenger ferries, the Pride of Provence and the Pride of Acquitaine, are being taken out of service in Dover.
The ferry operator has said the company was forced into making cuts because of increased competition from budget airlines and the Channel Tunnel.