[A 1] You needn’t write me another cheque. Just change the date and initial it; I’m in no hurry. He needn’t send it by air. He can send it by sea; You needn’t do it by hand. I’ll lend you my machine; You needn’t call me Mr Jones. We all use first names here; COLLEGE LECTURER: You needn’t type your essays but you must write legibly. [A 2] Tom doesn’t have to wear uniform at school; We don’t have to type our essays but we have to write legibly; When I’m an old age pensioner I won’t have to pay any more bus fares; Ann hasn’t got to go/doesn’t have to go to this lecture. Attendance is optional; When I have a telephone of my own I won’t have to waste time waiting outside these wretched telephone boxes; Ann doesn’t have to cook for herself. She works at a hotel and gets all her meals there. [A 3] I needn’t type/won’t/don’t have to type this report today. Mr Jones said that there was not hurry about it. I’m retiring. After Friday I need never go to the office again. I don’t have to queue for my bus. I get on at the terminus. (need not no podría usarse aquí.) [B] I didn’t have to wait long. He was only a few minutes late; When he was at university he didn’t have to/need to pay anything for his keep, for he stayed with his uncle.
[[A 1] Como se ha dicho, need not expresa la autoridad del hablante o consejo. [A 2] El resto de las formas expresa autoridad externa. [A 3] Con todo, a veces need not se usa para autoridad externa, como alternativa a las formas won’t/don’t need to o won’t/don’t have to. Esto es particularmente común en la 1ª PERSONA. Se puede usar need not para una acción habitual futura; no es posible usarlo para una acción habitual presente. [B] PASADO: en el pasado la distinción entre «autoridad del hablante» y «autoridad externa» desaparece y podemos elegir entre 3 opciones: didn’t have to, didn’t need to y hadn’t got to. No hay diferencia de significado, pero hadn’t got to no se emplea para acciones habituales. didn’t have to es la forma más usual.]
A Practical English Grammar (A.J. Thomson & A.V. Martinet) 