3. A police officer who makes such a transfer election shall, no later than the last day of the period of three months mentioned in paragraph 1(a) or (b), as the case may be (or such longer period as the Board may allow in accordance with paragraph 1), pay all pension contributions then payable by him under the 1988 Regulations, including any payment he has undertaken to make under regulation F5 (previous service reckonable on payment) of those Regulations, and all periodical contributions then payable by him under the Police Pensions (Purchase of Increased Benefits) Regulations 1988.