Hundreds more seafarers are at risk of being made redundant and replaced with cheaper agency staff if P&O Ferries’ mass sackings are not overturned, a rival operator has warned.

DFDS, one of the biggest passenger ferry operators out of Dover, has told ministers that P&O’s actions threaten to have serious repercussions to the rest of the British merchant navy.

The Danish shipping business is understood to have written to Grant Shapps, the Transport Secretary, warning him it may have no choice but to sack British staff and hire cheaper foreign labour if P&O gets away with its decision to axe 800 employees without a consultation.

It came as Mr Shapps told the House of Commons that P&O Ferries should remove British references from their ships if they replace sacked workers with non-UK staff. Unions claimed that the new agency workers are being paid as little as £1.80 an hour.

He said it would be “completely inappropriate” for the company to “attach themselves to this country” without having British workers.

The Spirit of Britain, Pride of Canterbury and Pride of Hull are among the names used for the operator’s ferries.

DFDS said that other companies could be forced to follow the example of P&O, and Irish Ferries before it, to scrap the “short-straits” model and replace it with an international shipping alternative that relies on cheaper agency staff from around the world, according to sources close to DFDS.

They said that DFDS would be under “huge commercial pressure” if P&O’s gets away with its plans to cut costs and creates an “unlevel playing field”.

DFDS employs about 8,500 people around the world, with several hundred British-based staff operating ferries from UK ports.

The intervention came hours before Mr Shapps faced a grilling in the House of Commons over the Government’s handling of the shock sackings last Thursday.