How to dress for evening theater in London

You'll be fine.

I’m male, so your husband will be fine. That’s what I’d wear, although I’ve also worn nice jeans.

I admire your stamina. When in London (or any other large city) I will get back to my hotel/apartment late afternoon, make a cup of coffee, and put my feet on the table. Then I would shower and put on fresh clothes to go out for dinner, a show, and a pint. Next day I will go touristing in the clothes from the evening before. So no more washing, but a chance to rest and going out in fresh clothes.

I'd probably be wearing shorts but as I can't stand opera I'd never attend. I have tolerated a normal theatre and you'll see the whole gamut of clothing, some people like to dress up to the nines, others are happy in jeans and a smart polo shirt. I've seen women in dresses, trousers, jeans, you name it, nobody is going to notice.

Can I get away with black pants and a nice top, my husband khakis and
a button down shirt? In the states I know that is considered ‘dressing
up’

Wear whatever you like for theatre in London. You both will be perfectly fine in the clothing you described above.

As an aside, perhaps "dressing up" is a regional distinction because your husband's khakis and a button down shirt is business casual. at least in Manhattan.

I went to a show in April. There were a few people that were dressed up, but most were comfortably dressed. I don't think that anyone really notices what you wear. I think those who dressed up, did so because they enjoy dressing up. There certainly wasn't any implied dress code.

It does tell you how times have changed. I remember as a child getting dressed in my best clothes before we went to the take the bus because we were going downtown. Such an event required our best!

Many of the theatres are not air-conditioned and get VERY hot and stuffy in the summer.

The only time I saw people really dress up for the theatre was to see Priscilla, Queen of the Desert. They were on the metro, wearing bangles, pink feather boas, sparkles and lots more. It made me a little sad that I hadn't booked to see the show.

When attending the theatre in London, I just wear the same "dressy" trousers that I use for touring, a nice shirt and black shoes. I haven't been to an Opera yet and that might be a bit more formal, but I'm certainly not packing a Tux!