There shall, in accordance with the directions of the Treasury, be transferred to the Exchequer from the Road Fund constituted under the [10 & 11 Geo. 5. c. 72.] Roads Act, 1920, a sum representing the amount of the cash balance and investments which were on the thirty-first day of March, nineteen hundred and twenty-seven, standing to the credit of that fund: Provided that such sum shall not exceed twelve million pounds.