But two decades after the sub-sea tunnel linked up Britain and France on May 6th, 1994, the doubters on the northern side of "La Manche" have largely been silenced.
Opponents had warned of a host of dangers, including drug trafficking, potato blight in the 'Garden of England' county of Kent, as well as an influx of French spiders and the arrival of bee-killing moths.
Others feared a fatal competitor for car ferries operating the Dover-Calais route and the possible bankruptcy of tunnel operator Eurotunnel.
The darkest nightmares were of tunnel walls collapsing due to flooding, earthquakes or bombs.
In February 1986, British transport secretary Nicholas Ridley sought to reassure concerned lawmakers, saying: "Will rabies come? Will the Russians invade along the tunnel? Should Britain remain an island?
"I sympathise with these emotional arguments but I do not believe that they are rational."
Some members of parliament called for all carriages to be sealed to prevent unscrupulous travellers dumping their rubbish, attracting foxes and other pests.
In fact, a wild rabid animal was found on a beach in southern England in 1996, the first trace of rabies in the country since 1922.
But vets revealed that the offending creature, a Daubenton's bat -- an insectivore very common in France -- was carrying a virus not transmissible to dogs, mammals, horses or foxes.
Most importantly, it had taken the aerial route across the Channel.
John Noulton, communications director of Eurotunnel, also sought to reassure claustrophobic critics that, although the tunnel was definitely dark, the train journey would be no worse than travelling on "a wide-body jet during the night".
Today, Eurotunnel supporters quote playwright William Shakespeare to describe the scare-stories as "much ado about nothing".
To be sure, it has not all been plain sailing.
There was a fire on a freight service in November 1996, while hundreds of immigrants housed at the Sangatte centre in Calais tried to rush the tunnel over Christmas in 2001.
The service suffers occasional cancellations and frequent delays, but the overall picture is positive.
There is an old joke that when fog descended over the Channel, the English declared the continent cut off, suggesting it was Europe that had been left all alone.
But times have changed, and strikes or traffic jams in the tunnel are met with impatience.
When a harsh winter caused the suspension of rail services and cross-Channel flights in 2009, the media spoke of Britons being "trapped".
In 1994, 75 percent of Britons said they didn't plan to use the sub-sea route to France.
Psychologists and psychiatrists commented on the possible trauma of anchoring the island to the European continent through a kind of giant umbilical chord.
And yet in October 2012, the year of the London Olympics, Eurotunnel celebrated its 300 millionth passenger.
The idea of a tunnel under the Channel was mooted by Napoleon Bonaparte in 1802, sparking horror in London where he was regarded as public enemy number one.
In 1858, prime minister Lord Palmerston rejected another plan, asking: "Why shorten a distance we already find too short?"
And in 1887, the Revue-Magasin de Normandie was still surprised by the "unexpected and fantastical fears of Great Britain's military authorities".
These days, Britain and France enjoy close defence ties, although the former is not quite ready to give up centuries of "splendid isolation".
If Prime Minister David Cameron is re-elected next year, he has promised to hold a referendum on Britain's membership of the European Union, where voters
could choose to quit.