The opening of the first bore at midday on 18 November 1963 paved the way for what is today the busiest links on the national motorway network, HA stated.

From the initial estimates of two million vehicles crossing each year it is now used annually by some 50 million.

Robert Goodwill, roads minister, said: ³The Dartford Crossing has proved to be a vital link on the M25 and a great investment in the economy, helping nearly 1.5bn vehicles cross the river Thames over the past 50 years.

"It continues to bring huge benefits to the economy and with these benefits comes demand. The Government is committed to doing all we can to ease traffic flow and improve journeys for the future."

Simon Jones, Highways Agency regional director added: "With tens of thousands of drivers relying on the crossing every day, it is vital that we keep the tunnels and bridge flowing. We understand the importance this route has for the local and national economy and have a team of operators and traffic officers who work around the clock to keep traffic moving."

Today’s crossing was designed to handle 135,000 vehicles per day but it is not unusual for 160,000 to occur, HA stated. In October 2014 a different, remote payment system will come into operation to reduce congestion and ease traffic flow.