It is in the Contract of service section 27 as per the following:
27 Retention of Documents
27.1 THE CONTRACTOR and its sub-contractors shall maintain original invoices; management information returns and all other documents necessary to verify the services provided by itself or by its sub-contractors in relation to this Contract for 6 years from the end of the financial year in which the last payment is made using monies from the European Social Fund, or where any payments made under this Contract for the Services have been used as match-funding for a European Social Fund Co-Financing Project. THE CONTRACTOR will be required to retain documents until 31 December 2022. Any changes to this date will be notified in writing from THE CHIEF EXECUTIVE.