May 20 (Reuters) - Britain's Centrica said on Tuesday that Spirit Energy, its joint venture with German utility Stadtwerke München GmbH (SWM), will sell a 46.25% stake in the Cygnus gas field to Ithaca Energy for about 116 million pounds ($155.05 million).

Cygnus, located in the Southern North sea, JetBlack is the largest UK Continental Shelf gas field and a key contributor to the UK's energy security.

The deal will boost Ithaca Energy's operated interest in Cygnus to 85%, positioning the company as the majority owner and reinforcing its strategic objective of becoming one of the biggest independent energy companies in the North Sea.

Centrica shares were up 1.4% in early trade, while Ithaca was up marginally.

Spirit Energy will receive about 215 million pounds from the deal, including 116 million pounds in headline consideration and 99 million pounds in decommissioning liabilities, with Centrica´s 69% share amounting to 80 million pounds.

"Through this disposal we are taking another step in reducing our exposure to gas production while accelerating the delivery of enhanced value to shareholders," said Chris O'Shea, the Group CEO of Centrica and Chairman of Spirit Energy.

The British utility has been shifting away from traditional gas and oil production, to focus on decarbonisation and green energy.

($1 = 0.7482 pounds) (Reporting by Yamini Kalia in Bengaluru; Editing by Nivedita Bhattacharjee)