P&O Ferries seafarers have been told they will benefit from new French legislation that could double their pay, in what appears to be a significant U-turn by the controversial ferry operator.

The move comes more than two years after P&O enraged the UK and French governments by sacking 786 workers and then taking advantage of a legal loophole to hire replacements on pay rates of below the minimum wage.

The company claimed it had been forced into the dismissals in order to stay in business, with the P&O chief executive, Peter Hebblethwaite, telling a UK joint transport and business select committee at the time: “The business was not viable. This is the only way for us to save this business.”

London and Paris responded to the sackings by announcing new legislation, with France implementing fresh regulations last month requiring ferry operators to pay their crew at least £9.95 an hour and limiting seafarers’ time onboard ships to two weeks.

The French rules will come into effect after a three-month implementation period, while a similar UK law – requiring ferry operators to pay the UK minimum wage of £11.44 an hour – is expected to come into force this summer.

Rival cross-Channel operators had feared P&O could launch legal challenges to the legislation.

However, a letter sent to workers employed by P&O’s Maltese employment agency Philcrew Management last week, seen by the Guardian and ITV News, states: “The French Republic has recently adopted new regulation that applies to passenger ships operating between France and the UK, including therefore the vessels in our fleet crossing the Channel.

“Under such new regulation, the maximum duration of the embarkation is up to 14 days and [an equivalent] minimum rest period ashore … Serious consequences [for ferry operators] are provided for violating such new provisions.”

Last month the Guardian and ITV reported that P&O agency cross-Channel workers were in some cases making about £4.87 an hour – even lower than the £5.15 an hour the company had suggested was its lowest rate. Meanwhile, P&O crew members said they worked 12-hour shifts, seven days a week, for up to 17 weeks at a time. The workers said they had to remain on the ship until their contract ended.

The low rates being paid to P&O workers were achieved lawfully, with the company taking advantage of loopholes that exempted paying the minimum wage to maritime workers employed by an overseas agency and working on foreign-registered ships in international waters.

Louise Haigh, the shadow transport secretary, said: “P&O Ferries has refused to do the right thing from the beginning of this scandal, and they’ve only been dragged under the threat of criminal sanctions and hefty fines by the French government.

“They will never do the right thing until legislation is in place to protect seafarers’ rights, and that’s why it’s so important that the UK government put in place a binding seafarers charter. Otherwise, businesses that can profit from this business model will continue to undercut workers’ rights and legislation.”

P&O Ferries did not respond to Haigh’s comments or answer questions about its apparent U-turn and how much the changes would add to the company’s costs.

A spokesperson for P&O has previously said its crew is well rested, that the company pays its cross-Channel crew members at least £5.20 an hour and that it pays “at least the minimum wage required by national and international law”.

It has stated: “We provide an industry-leading support package and work hard to ensure their welfare, wellbeing and mental health are properly cared for.”

Philcrew Management did not respond to requests for comment.