Britain's five biggest banks needed an extra £27.1 billion ($41.9 billion, 31.6 billion euros) at the end of 2012 to meet rules on capital backup, and must sell more assets and slash costs further, regulators said on Thursday.
The Prudential Regulation Authority (PRA), the Bank of England's banking supervision division, said in a statement that this figure compared with the previous estimated shortfall of £25 billion given in March.
Lenders already had plans in place to raise £13.7 billion of capital -- but needed to find another £13.4 billion, according to the regulator.
Barclays needed to raise £1.7 billion, while state-rescued pair Lloyds Banking Group (LBG) and Royal Bank of Scotland (RBS) needed to find another £7.0 billion and £3.2 billion respectively, the PRA said.
"All of the firms have been informed of their requirements and have produced for the PRA plans to meet them," it said.
"It is for the firms themselves to announce the actions they plan to take. In aggregate, the additional actions, which include disposals and restructurings, will generate the equivalent of an additional £13.4 billion of capital."
It added that the British units of Santander, HSBC, Standard Chartered and Nationwide Building Society could find the additional cash via their existing capital-raising plans.
The PRA is tasked with ensuring that all major British banks hold capital resources equivalent to at least seven percent of their risk-weighted assets.
"The PRA's assessment is that, at the end of 2012, five of the eight banks (Barclays, Co-operative Bank, LBG, Nationwide and RBS) fell short of this standard," it said in the statement.
"They had an aggregate capital shortfall relative to this standard of £27.1 billion."
The announcement came one day after British finance minister George Osborne ordered a review into whether bailed-out RBS should be split into 'good' and 'bad' banks, as part of the government's plan to return it to the private sector.