The Chicago Board of Trade's largest shareholder has called for the Chicago Mercantile Exchange to raise its offer with only a week left before a final vote on its proposed $10bn (€7.37bn) takeover, which has been backed by an influential proxy adviser group over a rival bid from the Intercontinental Exchange.

Caledonia Investments, a Sydney-based hedge fund that with 6.6% of shares is the CBOT's largest shareholder, has emerged as the latest to oppose the cross-town merger.