Name of movie (possibly british?) where a one-night stand ends in love?

I saw this movie several years ago. I don't remember too much about it, but it revolves around a couple who meet in a night, and spend the next day or few together, and fall in love. The actress has short cropped strawberry blond hair if I recall correctly. The movie is r-rated, but as much a comedy as a drama, and not obscene or anything. Help?