It rejected the challenge by London mayor Ken Livingstone and Bexley council in December as without merit.
Cory Environmental hopes to have the 72-megawatt incinerator on stream in 2010. It will burn 585,000 tonnes of municipal waste per year from the Western Riverside Waste Authority.
Mr Livingstone is "considering how to continue the challenge", said a spokesman.
Meanwhile, Waste Recycling Group has received planning permission for its 240,000 tonne incinerator in Salt End, Hull.
Hull City Council gave planning permission for the site in January, while East Riding of Yorkshire Council did so in December. The incinerator will straddle the border of the two authorities.
WRG has applied for a pollution prevention and control permit and hopes the plant will come on stream in 2010.