"This is an outstanding example of strong willingness to act despite difficult economic times," Hedegaard said in a statement.
The UK's decision confirmed that clever climate policies improved energy security and economic growth, in the Commission's view.
"With this decision, the UK seizes a huge economic and innovation opportunity that will make its economy more competitive in the future,' Hedegaard concluded.
Inter-departmental ministerial bickering had raised fears that the UK’s 2025 target might be watered down.
But in parliament on 17 May, the energy secretary Chris Huhne announced that a 50% emissions cut averaged over the years 2023-2027 would be entered into law.
"By making this commitment, we will position the UK as a leading player in the global low-carbon economy, creating significant new industries and jobs," said Prime Minister David Cameron said.
In 2010, the UK's emissions were 25% below 1990 levels. The EU's long-term goal, under a binding law, is to cut greenhouse gases by 80% by 2050.
Britain is one of only a handful of EU countries which want the bloc to sharpen its emissions cutting target to 2020, a shift many countries especially in eastern Europe oppose.
At present the EU says that it will only increase its ambition if all countries including the top two emitters the United States and China agree a new global deal to succeed the present Kyoto Protocol after 2012.
Many analysts say such a deal is out of reach, under UN climate talks long deadlocked over sharing the burden of emissions cuts between industrialized and emerging economies.
"We will review progress in EU climate negotiations in early 2014," said a UK government statement, adding that if the EU's industrial carbon emissions were falling slower than Britain's national trajectory then it would row back on its own targets.
That dampened some green groups' enthusiasm.
"The inclusion of a get-out clause, in case Europe doesn't cut emissions fast enough, creates needless uncertainty that could dent business confidence," said Friends of the Earth.
(EurActiv with Reuters.)