Spending amounts by Stronger In and Vote Leave are under investigation
The probe into the levels of spend has been announced by the Electoral Commission.
A total of more than £32m was spent on the campaign with the Leave side funded by donations totalling £16.4m exceeding Remain side's £15.1m, making it the most expensive referendum ever fought in British political history.Lib Dem spending is also under review.
The watchdog said invoices and receipts submitted by the Leave and Remain campaigns appeared to be incomplete and they were seeking further details in relation to certain payments.
Says Bob Posner, the Electoral Commission's director of political finance.
"Missing spending details undermine transparency and makes the returns harder for the public to understand,"
"Where it appears campaigners have not fulfilled their legal obligations, we have begun and will continue to take action to deal with this."
The BBC has more here
