Britain's top share index fell for a third straight session to a two-month low on Wednesday, with Admiral sinking after a downbeat trading update and Aviva slipping after outlining its turnaround targets. Car insurer Admiral slumped 3.3 percent after saying revenues fell in the first half of the year and there was no firm evidence of a return to growth in UK car insurance premiums. The company said it planned to launch its first ever bond of up to 200 million pounds ($340 million) to diversify its capital base and help prepare to meet Solvency II regulations in 2016. Oriel Securities repeated its "sell" rating on the stock, while Berenberg said a likely fall in margins was not reflected in current consensus earnings forecasts. "The market will be surprised that Admiral sees a need to raise debt. With the company forecasting falling margins and showing falling turnover, we believe these earnings forecasts will have to come down," Berenberg analyst Peter Elio