A key supply line linking Liverpool and Dublin has been indefinitely delayed after Peel Ports prevented a P&O Ferries vessel from sailing.

Peel Ports is the owner of The Mersey Docks and Harbour Company, which operates the docks at the Port of Liverpool.

The Norbay, a ropax vessel, is a ship carrying food, medicine and other supplies between the port of Liverpool and the port of Dublin.

However, it was stopped in Liverpool this morning after P&O was presented with what the company described as "a sudden demand for payment of almost £600,000".

There have been no sailings between both ports today. The sailings between Liverpool and Dublin represent between 20% and 25% of the number of sailings between the UK and the Republic of Ireland every day.

There are serious concerns among exporters and importers at the situation that developed today on Merseyside.

"It is worrying," said Simon McKeever, chief executive of the Irish Exporters Association. "We wouldn't like to see any diminished capacity or any backlog as a result."

P&O said it believed it owed much less than £600,000 to the port, and that the firm had been in ongoing discussions with the port authorities until their key contact was furloughed and the port neglected to tell them.

A spokesman for P&O said: "We have been in open discussions since this crisis began with all of our ports and network to ensure that we can manage payments while everyone deals with this unprecedented situation.

"We had asked for flexibility in the time required to pay but the Liverpool port refused to respond, even though we were committing to full payment.

"Then we learned that our point of contact had been furloughed and they didn't tell us," the spokesperson said. "The irresponsible and unnecessary actions of The Mersey Docks and Harbour Company Limited at a time of national crisis have closed an essential Liverpool-Dublin supply route, which means vital goods will not be able to flow between the UK, Ireland and Europe."