The British National Party has been accused of fraud.
The allegations were made on the BBC documentary show Panorama. According to the programme, the party treasurer submitted false invoices during the last general election campaign.
BNP leader Nick Griffin was said to have misled the Electoral Commission by encouraging a former colleague to alter an invoice involving EU money.
Mr Griffin denied the claim but offered to look into it.
Following the programme, which aired on Monday evening, the Metropolitan Police said it was investigating the "alleged offences" but said that no arrests had been made.
The anti-fascist campaign group Hope not Hate said the claims warranted "serious investigation by the Electoral Commission" and urged supporters to write to its chief executive.