Shares in US mortgage firms Freddie Mac and Fannie Mae dropped by as much as 50% in roller coaster trading last week amid concerns for their future. The US firm is the largest mortgage provider in america with almost £3 trillion dollars worth of home loans secured by the bank, almost 50% of the market. Speculation that US regulators were lat night preparing to step in to rescue the two compnanies, which are owned by shareholders but have government-sponsorship was greeted with concern in London city.