(Reuters) - Britain's National Grid said on Thursday it would raise about 7 billion pounds ($8.90 billion) via a fully underwritten rights issue of 1.09 billion new shares, as the utility firm steps up its investment in energy network infrastructure.

($1 = 0.7862 pounds)

(Reporting by Aby Jose Koilparambil in Bengaluru; Editing by Rashmi Aich)