A top official in Peter Mandelson’s European Union trade department has leaked highly sensitive commercial information in return for the promise of financial benefit.

In a six-month investigation, The Sunday Times tape-recorded Fritz-Harald Wenig, a trade director, passing secrets to undercover reporters posing as lobbyists for a Chinese businessman seeking insider information.

Wenig discussed the possibility of payment or taking a lucrative job with the businessman. He said he would decide further once he had provided “results”.

He leaked the names of two Chinese companies likely to get special status if the EU imposes a protective tariff barrier against Chinese candle-makers. The information is potentially worth millions to those trading with these companies.

His actions appear to be a breach of European commission regulations and raise questions about the standards of probity in Brussels, where civil servants formulate policy affecting trade worth billions with the world’s main trading blocs.

Yesterday, a spokesman for Mandelson, the trade commissioner, said he would launch a “comprehensive and thorough" investigation.

Alisdair Gray, director of the British Retail Consortium in Brussels, said: “Retailers throughout Europe will be shocked and infuriated that commercial secrets have been leaked from within the commission.”

Wenig, a former lawyer from Germany, is a powerful figure in Brussels. He was in charge of European tariffs on foreign imports for more than 10 years before becoming director of market access earlier this year.

In conversations with the undercover reporters whom he believed to be lobbyists, he also: Disclosed that Mandelson will back moves for further tariffs on Chinese footwear imports – the decision will be revealed to fellow commissioners on Wednesday. Offered to help a company linked to the lobbyists’ Chinese client if it applied for special status to exempt it from the footwear tariffs. Agreed to find out about other companies who may be given special tariff rates in a commission investigation involving aluminium foil.

Wenig denied this weekend that he had given away secrets. He described the information he had given as “semi public” and rejected the idea that it was commercially sensitive. He refused to comment on whether he had broken the rules.

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