Electricity transmission group National Grid said it was doubling the size of its U.S. operation by buying New York State electricity supplier Niagara Mohawk Holdings for £2 billion.

The cash and share deal will see National Grid take control of the second largest combined electricity and gas utility in New York State, which serves 1.5 million electricity and 540,000 gas customers.

The acquisition is the third major U.S. deal by National Grid in less than two years.

National Grid already owns New England Electric System and Boston-based Eastern Utilities Associates.

The company said the Mohawk acquisition would generate annual cost savings of around £60 million within four years.

The deal also more than doubles the size of National Grid's U.S.

operations and makes it a leading player in the North East U.S., becoming the second largest distribution business in the area.

It also creates the ninth largest electricity utility nationally in the U.S.

National Grid chief executive David Jones said the deal reinforced National Grid's position as a leading player in the North East U.S. and his goal of "becoming a top tier utility in the U.S. as a whole".