Police are considering whether to launch a full investigation into a complaint about the Liberal Democrats receiving £2.4 million from a donor later convicted of fraud.
The donation - the largest in the party's history - was given by businessman Michael Brown through his company 5th Avenue Partners before the 2005 General Election campaign.
Brown skipped bail while awaiting a fraud trial last year and was sentenced to seven years in jail after being tried in his absence.
A spokesman for City of London Police confirmed that a complaint had been received about the donation.
"We have received a complaint against the Liberal Democrats.
"As is standard procedure, we are looking at it before deciding whether to launch a full investigation," he said.
The head of the economic crime unit, Detective Chief Superintendent Stephen Head, told the BBC: "On the face of it they seem to be serious allegations."
The Lib Dems have insisted the donation was received in good faith and was "properly spent" on its General Election campaign but some of Brown's victims claim the party used their stolen money.
