UPDATE 1-UK Marchwood power plant to open in December

(Updates throughout)

LONDON, Nov 11 (Reuters) - Britain's Marchwood gas-fired power plant is to start commercial operations in December, Scottish and Southern Energy (SSE.L) said on Wednesday.

The company said in September the 840-megawatt plant near Southampton was expected to be in operation in time for its six month financial report published on Wednesday. [ID:nLB116605]

The 50:50 joint venture between SSE and ESB Inernational has been producing electricity during testing over the last few weeks but is not expected to open for business until next month.

"Marchwood is currently in its final commissioning stages. It's starting its final reliability runs in the next few days and assuming they all go to plan we should take it over fully sometime in December," SSE chief executive Ian Marchant said in a conference call on Wednesday.

SSE also announced plans on Wednesday to build a carbon capture trial unit at its Ferrybridge coal-fired power plant.

The 21 million pound ($35.16 million) pilot scheme to trap climate-warming carbon from the equivalent of about 5 MW of the plant's output is in collaboration with energy technology company Doosan Babcock. Trials are expected to start by early 2011 and run until the end of 2012.

German utility RWE (RWEG.DE) announced plans on Monday to build a 3 MW carbon capture pilot at its coal-fired power plant in Aberthaw in South Wales, within minutes of saying it had withdrawn from a UK government competition for funding for a 400-MW, full scale carbon capture and storage project. (Reporting by Daniel Fineren and Victoria Bryan, editing by Anthony Barker)