We are going to London the early part of May and am wondering if I should pack more casual clothing along with a few dressy items for evening or just keep it simple?

Well - it partly depends on what you mean by "casual". But there are no dress codes in London. (Well except for a few of the most high falutin' restaurants or opening night at the opera). Folks dress formally for work in some industries - but otherwise they keep it pretty simple/comfortable.

You won't be wearing shorts or capris - but casual is fine. Not a soul will care what you wear.

How old are you and what do you plan to do?

Will you go clubbing?
Go to church?
Go to hip hop concerts?
Eat in top restaurants?
Stay in high end hotels?

Each different activity would suggest a somewhat different wardrobe from the standard tourist/visitor clothes, but if you are doing fairly standard stuff, you can wear fairly standard clothes!

My suitcase for a trip to London would involve mostly what I wear at home: jeans (or other casual trousers) and casual tops most days, with a pair of black trousers and a nice top or two thrown in in case I feel like dressing up for a show or something. (All made out of almost wrinkle-free fabric!) As janis and Ackislander mentioned, if you plan to eat at very nice restaurants or stay at very nice hotels, you should check their dress codes. If you plan to go clubbing, etc., take whatever you'd wear clubbing at home.

The one thing I would do differently is to make sure I was wearing good shoes. You'll walk a LOT. But otherwise, as janis said, no one will care what you wear.

People in London do dress up more than those in the suburbs in the states, perhaps similar to working people in NYC or Boston. They are stylish and wear more shoes or boots rather than sneakers although you will see more casual wear on the weekends. Jeans are common, but they tend to be better tailored with a jacket or coat. The weather could still be chilly, perhaps in the 50's so bring layers. As someone may have mentioned, you seldom see shorts here. Longer capris or cotton slacks are more common in the summer months, but still tailored with sandles for women.

I ceased to worry about it one night in Paris. We fussed over what to wear to the Opera Bastille where I had slurged for the highest priced seats. So I had a suit and my wife had a nice dress.

We realized that we were overdressed when a Frenchman clad in a very format T-shirt sat down next to us.

If a T-shirt at the Opera Bastille in the highest priced seats is acceptable, I am not going to worry about what I wear!!

Except to a baby christening!!

Thanks everyone for your suggestions. This trip will be mostly sightseeing during the day, so we will dress in jeans and comfortsable shoes. In the evening, as at home when going out, I'll wear dressier pants with an appropriate top and heels. Since it will still be quite chilly, a few jackets are a must. I have a feeling people will just wear whatever they are comfortable in. Like janis said no one will care what you wear......sort of like in New York City, LOL!!!!

The days of having to dress up for 99% of the activities in London, just as in New York, are long gone.

I wear my usual casual attire to the theatre (clean (emphasis on clean) T shirt, blue jeans, sneakers) and to most of my pre theatre dining (usually Japanese places such as Wagamama, all I can afford in London in this day and age) and don't feel one bit out of place (exactly the same way I would go to the theatre on Broadway in NY)...this indeed is the 21st century.

Pretty much the only time you have to worry about any dress codes is if you go clubbing!

Don't worry about what to wear. You see anything and everything on the streets of London from frumpy and tacky to stylish to wild and crazy. If you plan to go to a club, follow the dress code, if you see a theatre show or go to a nice restaraunt, you should dress up a bit , same as here in the USA. Other than that, don't worry nobody will notice.

It has a maritime climate rather than a continental so layers, breathable and shower shedding. I find a hat works for me but hats do stand out

"if you see a theatre show... you should dress up a bit , same as here in the USA."

Only if you're determined to look like a hick American.

I've no idea whether Americans really do dress up to go to the theatre. Or why they do, if that's the case.

But we don't.