21U.K.If an individual is issued with a reference number for the purposes of paragraph 9(2), the individual must preserve, for the period of 6 years beginning with the date the application for the reference number was made, all such records as were required for the purpose of enabling the individual's relevant amount (see paragraph 9), and amounts A, B, C and D for the individual (see paragraphs 10 to 13), to be correctly calculated.