Shares in both companies slid a little today after Friday’s surprise of Thomson’s now-confirmed $17.6 billion takeover interest in Reuters gave way to one or two concerns over the size of the proposition. On Wall Street, Thomson was down 3.71 percent and Reuters 1.73 percent by mid-morning EST; at home in Toronto, Thomson was also down but Reuters closed up again, 2.31 percent, in London.

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The likelihood or otherwise of regulatory approval for such a deal has emerged as a thread. Forbes quotes a Merrill Lynch analysts’ note today: “A move to a global duopoly in market data would likely trigger a lengthy antitrust investigation on both sides of the Atlantic,” Merrill Lynch said in a research note.” It said the 34 percent share the tie-up would give Thomson-Reuters of the business information sector - marginally ahead of Bloomberg’s 33 percent, and enough to give just two providers a stranglehold.

“We would expect close U.S. and EC (European Commission) regulatory scrutiny,” said Credit Suisse analysts in a note cited by Reuters.

Forbes also suggested Reuters’ complicated editorial independence rules would prove a barrier but, as previously reported, the companies have pledged to retain the news agency’s independence.

Much of the skepticism emerged after claims investment banks would view the partnership uncomfortable. Inside Market Data editor David Anderson told The Guardian one unnamed bank was “pretty annoyed” about the loss of competition and would rather the market retains three information providers, with a newly beefed-up Thomson.

A disclaimer has now started appearing in Reuters’ own coverage of the story: “Reporters and editors involved in the writing and editing of this report may own Reuters securities and are bound by the Reuters Code of Conduct, which restricts dealing in securities in companies a journalist is reporting on.”