You are attending an English wedding, very cool! These weddings typically occur on Fridays, and what you wear generally depends on what time the nuptials occur:
Go for a buttoned-down, light-colored, collared shirt paired with khakis. If the wedding is more traditional, wear a tie. If the wedding is in the very early morning, you can skip the tie.
Opt for a classy, simplistic look that involves light makeup and flow-tastic dresses. Don’t wear a white dress for God’s sake, however pastel colors work well. Light colors are ideal for early morning dresses.
Evening/Black Tie Wedding
Wear a tuxedo if so inclined, though you will probably take the jacket off once the reception starts. A suit is ideal, such as black pants with a black jacket and dark blue or purple shirt and tie. Incorporating color into the mix is an excellent idea, as black and white are typically reserved for the bride and groom.
If the wedding is in the afternoon, opt for a suit without the jacket. This is especially true if the wedding is during the summer. Navy or black pants paired with a light green or blue shirt will look fantastic.
Feel free to wear dark hues, such as purple, black, etc. The reception is probably going to be dark, so amp up the makeup, wear your sexy heels, and otherwise have fun being a bombshell. Keep in mind the bride and groom’s families will be there so keep it tasteful, i.e. ensure your entire chest isn’t hanging out for the world to see. This doesn’t mean you can’t rock a tight dress…just be sure you can bend over in it.
As for English weddings at other times of day, go for whatever you feel comfortable in that’s still respectful. An A-line dress is a great choice, as is a dress with a sweetheart neckline. Think wedges in terms of heels, as they’re more comfortable and allow you to stand for longer periods.
Above all else, smile and be happy for the happy couple!