No undertaking shall be given under section 2 or 4 of the [1952 c. 54.] Town Development Act 1952 (Government and local authority contributions for the purposes of town development), and no payment shall be made in pursuance of any such undertaking, at any time after 31st March 1990; and that Act shall cease to have effect except for the purposes of any town development (within the meaning of that Act) in relation to which any undertaking has been given before that date under section 2 of that Act.