The $64,000 question facing investors in British banks is how the sector’s earnings will be affected as the credit bubble that has fuelled their growth over the past four years deflates.

Over the past six months, this has become a £40bn ($80.3bn) question. That is the value that has been wiped from the sector’s market capitalisation since it peaked in February. Even adjusting for the fall in the wider stock market over the same period, UK banks have seen a collective £23bn disappear from their combined market value in the past six months.