Class 3 contributions not paid within prescribed periods
50. Where a person was entitled to pay a Class 3 contribution under regulation 48, 146(2)(b) or 147, but he failed to pay that contribution in the appropriate period specified for its payment and his failure is shown to the satisfaction of the Board to be attributable to ignorance or error on his part which was not due to any failure on his part to exercise due care and diligence, that contribution may be paid within such further period as the Board may direct.