The public spending watchdog will examine the estimated £39 billion Brexit divorce bill to judge if it is reasonable.
The National Audit Office (NAO) confirmed it will scrutinise the financial settlement with Brussels after Treasury Select Committee chairwoman Nicky Morgan asked it to consider the “reasonableness of this payment” and assess how the figure was arrived at.
NAO chief Sir Amyas Morse said the watchdog had already started discussions with the Treasury and intended to report in March.
Prime Minister Theresa May told MPs last month the financial settlement as part of the Brexit process would be between £35bn and £39bn - as long as a deal on a future trading relationship was agreed.
Former Cabinet minister Mrs Morgan, who was a passionate campaigner for Remain during the referendum, said: “Various wide-ranging sums for the UK’s withdrawal payment to the EU have been bandied about.
“Last month, the Prime Minister told Parliament that the so-called Brexit divorce bill will be £35bn-£39bn.
“Parliament must be able to scrutinise the reasonableness of this bill.
“Accordingly, I have written to Sir Amyas to request that the NAO examines the withdrawal payment, including the assumptions and methodologies used.”
Sir Amyas said: “I can confirm that we intend to report on the main elements of the financial settlement with the EU.
“We are already in discussions with HM Treasury aimed at planning our work.
“I expect our report to be published in late March.”