ECB controversy over speech that sank the euro

The European Central Bank (ECB) has changed the way it publishes comments, just days after a speech by a key bank member gave away market-moving information to a select group of market participants.

Grumbles from the international investment community have been brewing this week after Benoit Coeure, a member of the ECB's Executive Board, said in a talk late Monday that the central bank would "front-load" its asset purchasing program during the summer months to counteract weak liquidity.

However, a transcript of the market-moving comments was not published by the ECB until around 7 a.m. London time the following morning – when it caused the euro to plunge by around 1 percent against the dollar.

Read MoreEuro slides, Treasurys rise as ECB gets heavy on QE

An ECB spokesperson told CNBC via email that it had intended to publish the speech when it was delivered, but did not because of an "internal procedural error."

An employee talks on the phone as he views trading screens at the offices of Panmure Gordon and Co.
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An employee talks on the phone as he views trading screens at the offices of Panmure Gordon and Co.

Its failure to do so potentially gave those in the room a head start on the euro's plunge, despite the ECB regularly detailing that it could perform such a move in the fine details of its quantitative easing (QE) program.

"It's naughty and cheeky to give this sort of information," Claus Vistesen, the chief euro zone economist at Pantheon Macroeconomics, told CNBC via telephone Thursday.

On Wednesday - just two days after the controversial speech - the ECB announced that it would stop sending embargoed copies of speeches to journalists. The central bank did stress, however, that this issue had been under consideration for several months.

Economist Vistesen said it was highly probable that Coeure's comments were innocent and that he didn't realize the impact they would have. But he speculated that investors in the room would likely have profited from the news.

"They would have been on the button," Vistesen said. "They would have made a little money." (Tweet This)

The organizers of the event told CNBC via email that Monday's audience included academics, policymakers and practitioners and the program, with a list of speakers, was uploaded online.

However Ashok Shah, an investment director at London & Capital, told CNBC Thursday it would be hard to determine which – if any — had profited from the comments.

Read MoreRapidity of bond selloff is worrying: ECB's Coeure

Valdis Dombrovskis, the vice-president for the euro and social dialogue at the European Commission, wouldn't been drawn on the issue when asked about a possible investigation Thursday, telling CNBC that it was a matter for the ECB as an independent body.

It's not the first time that questionable links between central banks and market participants have surfaced. A report by U.S. Federal Reserve staff in 2012, for instance, concluded that a leak of information from a closed Fed policy meeting was due to "unintentional or careless" contact between officials and the press and a brokerage firm.