WHILE ads for “Brideshead Revisited” feature Emma Thompson, the real star of the movie is Hayley Atwell, a voluptuous brunette whose character is torn between her love for an atheist and her Catholic faith. After the Cinema Society’s premiere of the Miramax film Tuesday night, she was asked about guilt, the theme of the Evelyn Waugh novel on which the picture is based. “I don’t feel guilt,” she declared. “I had very tolerant parents.” Partying later on the Gramercy Park Hotel roof were fellow Brits Matthew Goode, Alexandra Richards, Nigel Barker, Jonathan Cake, Hamish Bowles, Rufus Albemarle and Miramax president Daniel Battsek.