Need not + have + past participle. Уроки современной разговорной грамматики английского языка от репетитора - English Grammar tuition on line via Skype
If we say that somebody need not have done something, we mean that he or she did it, but it was not necessary. Типа, "зря это сделали"
- You need not have woken me up. - Мог и не будить меня.
I don’t have to go to work today. - I needn’t have cooked so much food. - Не надо было готовить так много еды.
Nobody was hungry. - They need not have come all this way. (= They came all this way, but it was not necessary.)
- We need not have waited for his approval. (= We waited for his approval, but that was not necessary.)
- You need not have bought a new car.
- You need not have paid for that call.
Note that need not have does not mean the same as did not need to. When we say that somebody did not need to do something, we are simply saying that it was not necessary (whether or not it was done).
Compare:
- I needn't have watered the flowers. Just after I finished, it started raining.
- It started raining, so I didn't need to water the flowers.
- I need not have bought it. (= I bought it, but it was not necessary.)
- I didn't need to buy it. (= It was not necessary for me to buy it.)
