JP Morgan's weak trading profits in July and August, added to an already costly telecoms exposure, have already resulted in a profit warning, a brace of rating downgrades and a fall in its stock and bond prices.

After the US stock market closed on Tuesday Bill Harrison, who heads the the US firm, said third-quarter profits would be hit hard by poor trading profits and exposure to the beleaguered telecom industry, where the bank is one of the biggest lenders.