Barclays shares tumble following £12.8bn shortfall news

This comes after the Prudential Regulation Authority issued more stringent capital requirements to ensure banks are protected from the risk of investment losses, even in the event of another financial crisis.

The PRA requires all banks to have a minimum leverage ratio - a measure of financial health indicating the amount of capital held by the bank relative to its gross lending - of 3%. Under these new rules, Barclays was found to have a capital shortfall of £12.8bn.

Barclays chief executive Antony Jenkins said the plan would not reduce the supply of loans to provided by the bank, and commented: "I am certain the decisive and prompt action we are taking will leave Barclays stronger."

Barclays fell 2.7% to 311.3p, which was the biggest loss on the main London index by a clear margin.