Guinness purchase is expected to be challenged.

Financial analysts said a merger agreement between Arthur Guinness & Sons and Distillers Co. would create a company controlling nearly 40% of the British market for Scotch whisky and could face stiff challenges from Britain’s antitrust agency, the Monopolies and Mergers Commission. Ernest Saunders, Guinness’ chief executive, discounted the possibility of an antitrust review. Guinness announced an agreement Monday to acquire Distillers for about $3.21 billion at current exchange rates.