National Grid reports lower-than-expected H1 profit

(Adds details)

Nov 9 (Reuters) - British power grid operator National Grid (LSE: NG.L - news) Plc reported a slightly worse-than-expected fall in half-year profit on Thursday hurt by weakness in its UK electricity transmission business.

Adjusted operating profit fell 12.8 percent to 1.26 billion pounds ($1.66 billion) for the six months to Sept. 30.

That was below the 1.29 billion forecast in a poll of 7 analysts.

The company, which maintained its full year outlook, said it expects capital investment to rise to over 4 billion pounds after a first-half outlay of 2 billion pounds, up 7 percent from a year earlier or 4 percent at constant currency rates.

At its UK electricity transmission business, adjusted operating profit fell 11.5 percent to 540 million pounds, missing the 575 million estimate by analysts.

The business was hit by lower allowed base revenue and higher costs.

Profit from its U.S. Regulated business, which operates electric transmission facilities and gas distribution network in some U.S. states, rose 19.2 percent to 526 million pounds, topping estimates of 443 million.

Full year performance in the U.S. business is expected to improve driven by a full year of new rates in its downstate New (KOSDAQ: 160550.KQ - news) York gas and Massachusetts Electric businesses, National Grid said.

($1 = 0.7607 pounds) (Reporting by Arathy S Nair in Bengaluru; editing by Jason Neely)