QE2 is the same as most other ships. There are casual nights, informal nights and formal nights. Daytime wear is casual. You can find out far more in the brochure, and their web-site and in the pre-cruise booklet they send you.....Nei.
From the Cunard website:
Do I have to dress for dinner every evening?
One of the great thrills of a Cunard cruise is the sheer glamour of the evenings. Generally, evening dress may be either formal, informal or casual when your ship is at sea, and informal or casual when your ship is in port. There will be a maximum of three formal nights in a week. Evening attire, effective from 6pm, will be specified in your ship’s Daily Programme, delivered to your stateroom each day. Dress codes are defined as follows:
Black tie or formal dark suit for men. Evening dress or other formal attire for women.
Jacket and tie for men. Cocktail dress or trouser suit for women. No jeans.
Jacket, no tie required for men (no jeans or shorts). Dress, skirt or trousers for ladies