The cost of trading shares has risen because of a triple whammy of rising stock market volatility, thin trading volumes and weakened investment bank balance sheets, with some warning the shift could be permanent.

Since the summer, investment banks have widened the difference between the price at which they will buy and sell many stocks – the bid-offer spread – to compensate for the risk of losing money if share prices move wildly, or if it becomes hard to match an order in the market. Wider spreads mean investors pay more to buy a stock, and make less when they sell.