(FORTUNE Magazine) – -- The London stock market has hurdled one of the biggest barriers to constructing a tunnel under the English Channel. Investors in November agreed to buy the entire $626 million British portion of a $1.4 billion stock offering by Eurotunnel, the Anglo-French company with a monopoly franchise to build and operate the so-called Chunnel. The success of the issue ensured that a global consortium of 200 banks would loan the project up to $9 billion as promised. Construction on the tunnel itself may begin as early as mid- December, and some preliminary digging is already under way. French support for the offering was never in doubt, in part because the government has considerable leverage with French financiers. But the British, who have long resisted any kind of physical yoke with the Continent, dragged their feet. Underwriters had to wheedle support from the big British financial institutions, which are still smarting from Meltdown Monday and from heavy losses in the $12 billion British Petroleum privatization issue. Maybe the investors should have resisted a little more. Eurotunnel stock will pay no dividends until at least 1994, a year after the twin-tube railway is scheduled to open. The underwriters' analysts optimistically forecast a potential capital gain of as much as 40% per year in the interim, figuring the stock will go up as the tunnel nears completion. Recently Eurotunnel boosted its projections of tunnel use as much as 20%. Says Richard Hannah, an analyst for Phillips & Drew, a London brokerage house: ''It certainly undermines the credibility of a forecast to change it so much in one year.'' The biggest worry to investors eager for the dividends is whether workers can punch a 31-mile cavern through subaqueous chalk in the 5 1/2 years allotted. The precedents are hardly encouraging. Construction of a tunnel of similar length joining the Japanese islands of Honshu and Hokkaido began 23 years ago and has cost roughly $5 billion and several dozen lives. Whenever the Chunnel is finished, a small but loyal group of patrons is assured. To enhance its stock, Eurotunnel is offering investors who pony up $9,300 for 1,500 shares in the public offering a lifetime of free Chunnel trips.