Triton Knoll's capacity is now expected to range between 600 and 900 megawatts (MW), instead of the original 1,200 MW, RWE's renewable energy subsidiary Innogy said in a statement.

Offshore wind farm developers have now largely finalised British site assessments and industry experts say that project capacity reductions and cancellations are inevitable as investors decide which wind farms are best to take forward.

"The recent optimisation work is part of a project review to make the site more competitive and more economic in line with government proposals to bring down the cost of offshore wind," RWE Innogy said.

At the end of November the company scrapped plans to build one of the world's largest offshore wind farms in British waters - the 1,200 MW Atlantic Array - saying it no longer made economic sense to build it.

British utility Scottish Power subsequently also announced the cancellation of a large UK offshore wind farm and peer Centrica decided to sell one of its projects to DONG Energy.

Britain is the world's biggest offshore wind market and aims to defend its lead by multiplying current capacity to 10 gigawatts (GW) by the end of the decade.

Offshore wind farms are some of the most expensive renewable energy projects because they are built far out at sea, but government subsidies are designed to help developers regain some of their investments.

The government is spearheading a campaign to bring the cost of building offshore wind farms below 100 pounds per MWh.

(Reporting by Karolin Schaps; Editing by Pravin Char)