The Serious Fraud Office has confirmed that it is making a preliminary assessment before deciding whether or not to hold a full inquiry.
The BBC admitted that staff knowingly withheld money meant for charity after internal auditors carried out an investigation into the broadcaster's phone voting systems last week.
The money was generated by callers voting after phone lines had closed on about 20 shows, believed to include Eurovision and Fame Academy, between October 2005 and September 2007.
Voters were still charged around 25p per call but the money went into BBC Worldwide's bank account rather than to the charities.
An internal audit showed that a number of staff working in Audiocall, part of BBC Worldwide, repeatedly kept money back.
The BBC said that the "small number" of people involved face disciplinary action and possible dismissal.
The broadcaster is already facing fines of up to £250,000 from regulator Ofcom over previous scandals involving Blue Peter, Comic Relief and Children in Need.
The Serious Fraud Office is also studying phone-in scandals at .
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