P&O Ferries has cast the planned £300m privatisation of Dover Harbour into doubt over claims of overpricing.

The ferry company, which is Dover Harbour Board’s largest customer, has lodged an official complaint with the UK government over the port’s prices.

Helen Deeble, chief executive of P&O Ferries, has submitted a letter to shipping minister Mike Penning, advising him that talks with Dover had broken down and that the company would be submitting a pricing complaint under Section 31 of the 1964 Harbours Act, reports The Telegraph.

It is the most serious development yet in the growing row between the port and its three major shipping customers – the others being SeaFrance and Norfolkline – which collectively make up 80 percent of Dover’s traffic.

Norfolkline has also noted its plans to lodge a similar complaint, and could take the case to Brussels under European competition law.

The shipping lines allege that Dover wants to use £60m paid by them through higher tariffs to contribute to its planned privatisation – rather than spend it, as agreed, on a second ferry terminal. They are also angry at a proposed 33 percent increase in tariffs.

Ms Deeble told The Telegraph: “We have given Dover every opportunity to address our concerns but they have not done so and we are at the end of our tether.”

The Government’s plans for the privatisation of UK trust ports, including Dover, could be clarified at next Tuesday’s emergency Budget.