The Royal Opera House abolished its formal dress code years ago, and the result is a room that runs from denim to dinner jackets. Both are technically welcome. But an opera house is one of the last interiors in London built entirely for occasion — and dressing for it is not obedience, it is participation.
What the room expects
Nothing, officially. In practice the stalls and boxes lean dark and considered: suits without ties, midnight colours, proper shoes. A jacket puts you comfortably in the middle of the room. You will not be turned away for less — you will simply photograph the evening differently in your own memory.
What it rewards
Wool, silk, structure — things that hold a line under warm light. For women, a dress that can sit for three hours and still stand well at the interval. For men, the simplest good suit and the discipline to skip the novelty. The opera is long; comfort that looks like elegance is the whole trick.
The interval
Book the interval drinks when you book the tickets — the good bars sell out before the overture. The Paul Hamlyn Hall at champagne hour, glass roof going dark overhead, is one of the finest rooms in London to stand in for twenty minutes. It deserves better than a rushed queue.
Beyond Covent Garden
Glyndebourne in summer still means black tie and lawns; the Coliseum is a shade more relaxed than the Royal Opera House; first nights everywhere run more formal than the run. When in doubt, dress up a step. Nobody has ever regretted being the best-dressed person at the opera.
An opera seat is better with someone in the next one. Ask, if the season suits.