The Metropolitan Police and the Charity Commission are looking into an allegation of fraud potentially involving hundreds of thousands of pounds at the London South East branch of the RSPCA.
Two men were arrested by the police in September in relation to the allegation and remain under investigation.
According to the Guardian, former RSPCA trustee Ivan House estimated the scale of the suspected fraud to be between £330,000 and £450,000.
An RSPCA spokesperson said the charity was undertaking a financial review after “concerns were raised” about the running of the branch, which is a charity registered separately from the national organisation.
They added: “The issue has been referred to the police and we are not in a position to comment further but we would like to reassure our supporters that the branch continues to operate as usual.”
According the Charity Commission's charity register, the branch's annual accounts for the year to December 2017 are currently 166 days overdue.
A Commission spokesperson said the regulator opened a regulatory compliance case to assess the charity’s response after a serious incident was reported to it.
They said: “We expect the trustees to submit the findings of their internal investigation once complete, which we will review, as well as any necessary policies and procedures, including around financial controls, to ensure the charity has acted appropriately.”
The Commission criticised the charity last year over "concerning gaps in record keeping" at its Tunbridge Wells and Maidstone branch.
A spokesman for the Metropolitan police said: “Police received an allegation of fraud on 3 September 2018 relating to a charity based in Norwood, south-east London.
“On 12 September two men – aged 44 and 55 – were arrested on suspicion of fraud. Both have been released under investigation. Enquiries continue by officers from the south area command unit.”