12:45 A.M. LONDON A Louise Brooks look-alike glides onto the crowded dance floor of Throgmortons, the beads of her dress flapping in time with Irving Berlin's classic "Top Hat, White Tie and Tails." She extends her hand to David Piper, the dapper host of the Modern Times Club. His monthly guerrilla-style soirées, which celebrate the Jazz Age, are advertised by word of mouth only (tickets sold at; $18). "Not since Errol Flynn rode piggyback on Katharine Hepburn into Cole Porter's swimming pool has there been such an affair," Piper says, admiring his 250 festively attired guests as they break into the Charleston after a three-course meal. The British scenester also holds a smaller Tuesday-night gathering, Rakehell's Revels, at Oscar Wilde's old haunt, the Grill Room at the Café Royal. Proper spirit required. —VICTORIA DE SILVERIO