The BBC joined a team from the SFO as they put on stab vests and raided a company office at a business park in Cannock.
Lead investigator Ross Corrigan said the SFO suspected this was a ”sophisticated and systemic fraud within the government’s Energy Company Obligation 4 (ECO4) scheme which was designed to help people in fuel poverty”.
“And yet here we have suspected criminality which might have exploited that good cause,” he said.
The ECO4 programe began in 2022 and involved the installation of heat pumps, solar panels and insulation in more than 300,000 homes.
It was targeted at elderly or vulnerable people living on low incomes.
The scheme, which has since closed, was funded through a levy on household energy bills and has cost £4bn.
The SFO said that three companies were involved in the fraud: JJ Crump of Sheffield, South Coast Insulation Services in Fareham and Cannock-based Warmfront.
South Coast Insulation Services went into administration in February.
The SFO alleged the three businesses claimed money for insulation work on 5,000 properties they never installed.
The BBC has contacted the firms for comment.
The SFO said it wants installers and assessors who worked on these contracts to contact them at confidential@sfo.go.uk.
Sir Geoffrey Clifton-Brown MP, chair of the Public Accounts Committee, said the SFO investigation showed that the ECO4 scheme was looking increasingly like a ”charlatan’s charter”.
He said the “sheer amount of money” that may have been fraudulently claimed, estimated at £44m, “serves only to underline further that the known levels of fraud in the scheme, as our committee warned earlier in the year, must be being significantly underestimated”.
Almost all of the external wall insulations delivered under the scheme – 98% – required repairs, according to the a report by the National Audit Office.