The European Commission has narrowed its review of the proposed merger of Deutsche Börse and London Stock Exchange Group, focusing attention primarily on whether the proposed tie up would give the combined company too much power over the clearing of derivative products.

The commission opened its anti-trust probe into the proposed merger in September, concerned that as the largest Europe-exchange operator the combined company could potentially block rivals form competing in areas of clearing functions, derivatives, repurchasing agreements, German stocks and exchange-traded products.