A leading private sixth form college featured on a TV documentary is at the centre of a police investigation into suspected fraud.
South Wales Police said the probe was launched after a referral was made about suspected financial irregularities at Cardiff Sixth Form College.
The Charity Commission said it has opened an inquiry into the running of the college, adding there are concerns about its governance, financial management and transactions between the charity, which is responsible for the college, and some former trustees.
College principal Gareth Collier told the Press Association there was no issue with its teaching, learning and pastoral care.
The college, a fee-paying school for 16 to 18-year-olds, regularly records some of the highest A-level results in the country. Earlier this year it was the subject of the BBC documentary Britain's Brainiest School.
In a statement, police said: "South Wales Police officers are investigating a suspected fraud at Cardiff Sixth Form College on Newport Road.
"The action follows a referral made to South Wales Police with regard to suspected financial irregularities at the college.
"An investigation into the allegations was launched by South Wales Police Economic Crime Unit and the Charity Commission have appointed an interim manager to take over the administration of the college."
Mr Collier said: "It is business as usual at the college. We continue to deliver a high-quality education and there is no question at all of anything untoward in the activities of the college in regard to teaching and learning and pastoral care.
"We are pleased to be able to offer students an outstanding education with excellent outcomes in terms of academic results and university placements.
"The Charity Commission has identified regulatory concerns about the charity's governance, financial management and significant related party transactions between the charity and some of its former trustees. The Charity Commission has appointed an interim manager, in the person of Emma Moody of Bond Dickinson, to see us through this period of change."
The commission began looking into the college in April after the charity responsible for its running failed to submit its accounts.
It said: "The charity does not appear to have identified and/or managed conflicts of interest and there have been significant high-value transactions which may not have been properly authorised."
As a result, there will be a further inquiry looking at issues such as "whether there has been any unauthorised private benefit to trustees (current and former) or connected parties", the financial management of the charity and whether there has been any misconduct or mismanagement by trustees.
"This inquiry is about the governance and financial management of the charity not about its provision of education," the commission said.
It added: "The commission is also aware that South Wales Police are investigating a number of allegations concerning historic financial irregularities. We are liaising and working closely with South Wales Police as part of our investigation.
"The commission stresses that opening an inquiry is not in itself a finding of wrongdoing. The purpose of an inquiry is to examine issues in detail and investigate and establish the facts so that the regulator can ascertain whether there has been misconduct and mismanagement; establish the extent of the risk to the charity's property, beneficiaries or work; decide what action needs to be taken to resolve the serious concerns, if necessary using its investigative, protective and remedial powers to do so."