The legitimacy of the $100 billion (£60 billion) carbon-trading market has been called into question after the world’s largest auditor of clean-energy projects was suspended by United Nations inspectors.

SGS UK had its accreditation suspended last week after it was unable to prove its staff had properly vetted projects that were then approved for the carbon-trading scheme, or even that they were qualified to do so.

The episode will be embarrassing for European lawmakers in the run-up to the global climate summit in Copenhagen, where they will attempt to lure big polluters such as America and China into a binding agreement to replace the Kyoto protocol. SGS is the second such company to be suspended – Norway’s DNV was penalised last November for similar infractions.

The EU’s carbon-trading system, which puts a price on pollution through carbon permits that can be bought and sold, is the key element in Europe’s fight against climate change.

About a fifth of the $100 billion of credits traded annually come from projects funded under the Clean Development Mechanism (CDM). The heavily criticised programme allows industrialised countries to offset their pollution by buying “certified emission reductions credits” generated by low-car-bon schemes in the developing world. China and India are the biggest generators of the credits: more than 900 projects are now running, producing billions of credits, with thousands more in the pipeline.

Critics say the system is not sufficiently policed and allows western polluters to buy their way out of more costly carbon-cutting measures.

All such schemes must first be approved by organisations such as SGS. DNV was the single biggest auditor until it was suspended last year, when much of its workload was shifted to SGS, which was simply unable to cope.

Simon Shaw, chairman of EEA Fund Management, a backer of emission-reduction projects and an investor in Climate Exchange, the carbon-trading platform, said: “There was obviously a lack of resources. We knew this was coming.”

UN inspectors said they found six irregularities in a recent spot check. The firm has now rectified these, but remains suspended until the UN verifies sufficient changes have been made. SGS could not be reached for comment.

Lawmakers are expected to reform the CDM in Copenhagen in December. A research firm that tracks trends in clean energy and carbon trading has been put up for sale with a £30m-£40m price tag. New Energy Finance was set up in 2004 by Michael Liebre-ich, a former McKinsey consultant who owns a key stake.

Its backers include former Reed Elsevier boss Sir Crispin Davis and Mike Luckwell, a one-time investor in Hit Entertainment. The corporate finance firm Quayle Munro was brought in to advise on options after takeover approaches were received.

Energy and Environment, page 13

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