The banking giant said a raft of so-called sovereign wealth funds and foreign groups had agreed to pump money into the bank, including the Qatar Investment Authority and Japanese banking giant Sumitomo Mitsui Banking Corporation in return for discounted shares.

Barclays added that existing shareholders will also be offered the chance to buy shares under the scheme.

Challenger, a group backed by the Qatar royal family - His Excellency Sheikh Hamad Bin Jassim Bin Jabr Al-Thani and his family - have also pledged cash to Barclays, according to the group.

The group said all existing investors will be able to take part in a "claw back" of up to £4 billion worth of shares, although the full amount has effectively been underwritten by the QIA, Challenger and existing Barclays institutional shareholders China Development Bank and Singaporean government-backed fund Temasek.

Sumitomo, which is Japan's third largest bank, has agreed to invest around £500 million by buying shares at a 4.7% discount to Tuesday night's closing price, which is not open to an investor clawback.

John Varley, group chief executive of Barclays, said: "Through our capital raising today we strengthen our capital base and give ourselves additional resources to pursue our strategy of growth through earnings diversification.

"We position ourselves to capture opportunities for new business at attractive margins in our retail and commercial banking businesses and in investment banking and investment management.

"Our ability to capture the opportunities is reinforced by the new and strengthened relationships we have announced."

Shares in Barclays rose 5% in early trade as the market cheered confirmation of the widely-speculated cash raising scheme.