What to wear in London inApril (next week)?

Any suggestions for what to pack for a trip to London? I am wondering what the fashion is like there this time of year. Do people wear jeans? What about going out at night? I have black clogs and Converse for sightseeing, ballet flats for dinner and highheeled boots for going out. I am looking for a warm rain jacket. Will I need a warm coat or will a trench style be warm enough? Hate to overpack, so any help will be fab.