Talks over a potential merger between German exchange group Deutsche Börse and transatlantic counterpart NYSE Euronext are believed to have stalled over the relative stock market worth of the groups in the latest example of valuations confounding what would be a landmark merger.

Sources close to the exchanges said this morning that they had held informal talks over a potential tie-up "recently", resurrecting a dialogue that took place at the end of last year, but that no decision had been made and no announcement was imminent.