The Markit iBoxx Sterling Corporate Bond Index has fallen 10.2% so far in September to a price of 296, putting it on course for its biggest monthly slide since at least 1999. The ICE BofA Sterling non-Gilt Index, which measures the prices of investment grade debt, is headed for its worst monthly performance since records began in 1997. It is down 9.8% in September with a price of around 337 at Tuesday's close.

(Reporting by Tommy Reggiori Wilkes and Lucy Raitano; editing by Dhara Ranasinghe)