It was heralded as the first bus transport system of its kind in the world but lasted little under two years and only brought in £45 a month.

When the long-awaited first Dartford Tunnel opened in 1963, linking Kent with Essex via a bored route under the River Thames, it cost £13m and was nearly a mile long.

At the time, the number of vehicles using the tunnel was estimated at around two million a year. Today that figures is thought to be closer to 65 million.

On November 18 1963 a familiar sight formed in front of the newly excavated route as motorists queued in large numbers to access the river crossing.

The main difference being that the orderly queue was made up of people who actually wanted to be there to catch a first glimpse of the engineering feat – and not stuck in a snaking six-mile tailback as is often the case today.

But one thing that hasn't changed over time is the need to be able to offer safe thoroughfare for cyclists.

From the early planning stages, overseen by the Ministry of Transport, it was thought heavy traffic through the narrow tunnel would pose significant risks to those using two wheels rather than four to get across.

The result was the Dartford Tunnel cycle bus service which consisted of a fleet of five custom made double deckers to carry bikes across the river from 6am until 10pm at night.

In total, the adapted buses cost little more than £12,000 and were heralded as the first of their type in the world.

On board the bus the lower deck was converted to carry bicycles of various sizes, while the upstairs was used to ferry the cyclists.

Towards the back of the bus was a large space to accommodate tricycles, tandems, sidecars, and even baby's pushchairs.

The upper deck provided seating for 33 passengers and was accessible via a series of steps built into the side of the bus.

In a somewhat bizarre move – and unlike any bus currently in operation – passengers were unable access the bus from the ground.

Instead, special platforms were created either side of the tunnel, similar to mounting blocks used by horse riders, to aid cyclists onto the staircase from below.

But according to the National Archives, the ill-fated Dartford Tunnel cycle scheme proved too costly to run and ran into certain operational difficulties.

Only days before the service was due to start running in October 1963 safety concerns were flagged.

With no doors to the upper deck of the bus, a restricted view of the passenger area from the driver's seat and no conductor to supervise journeys, the Ministry of Transport had to rely on signage and the common sense of passengers not to fall off.

Once inside the driver would be unable to stop should anything happen.

Despite this when the tunnel opened a service started consisting of four buses – with one in reserve – running every six minutes.

But transport planners had miscalculated how many cyclists would require the service and just five months later in April 1964 the service was reduced down to one bus, before being cancelled altogether in 1965.

Costs were also a major factor in its demise with £2,550 being paid out on the service per month, with only £45 per month being brought back in revenue.

When the service was dropped it replaced Land Rovers with trailers instead.

And even today that remains the case with it being possible to hitch a ride on your bike for free, avoiding the £2.50 toll charge now in place.

To access the service you simply have to call a number between certain times via designated drop off and pick up points located at either side of the route.

The first Dartford Tunnel was opened in 1963 and is the most easterly crossing of the Thames, being 16 miles from the centre of London.

A second tunnel was added in 1980, and was followed by the Queen Elizabeth II Bridge which opened in 1991 with the tunnels taking traffic north, and the bridge bringing it south. Together they both form part of the M25 orbital road network.