LONDON - Four people were arrested and addresses raided in Britain, the Netherlands and Belgium in a joint Anglo-Dutch investigation into biodiesel trading at British road fuel supplier Greenergy, the UK’s Serious Fraud Office (SFO) said on Thursday.

The SFO said the individuals had been released without charge and that five British sites were among those searched on April 30 in an investigation into Greenergy and unidentified third parties.

Greenergy, which is majority-owned by private equity company Brookfield Business Partners and 15% management-owned, said it had only become aware of the inquiry into aspects of its biodiesel trading business and other parties on April 30.

“The company takes these matters very seriously and is engaging and co-operating fully with the authorities,” it said in a statement. “As this is an ongoing investigation, we are not permitted to give any further details at this time.”

When asked about the SFO-Dutch inquiry, Varo Energy, a European refining firm owned by oil trader Vitol Group, U.S private equity firm Carlyle Group and Dutch firm Reggeborgh, said it had been asked to collaborate “in an on-going investigation”.

“As a matter of policy, Varo always cooperates fully with the relevant authorities in any jurisdiction in which it operates,” a spokeswoman told Reuters. She gave no further details.