Treasury officials are negotiating terms of the recapitalisation with the banks
Up to £50bn of taxpayers' cash is to be injected into four of Britain's biggest banks through the government's rescue package, the BBC has learned.
Royal Bank of Scotland (RBS), HBOS, Lloyds TSB and Barclays are being told by Treasury officials to seek the cash to shore up their balance sheets.
An announcement is planned before the markets open on Monday, according to BBC business editor Robert Peston.
Meanwhile, Lloyds TSB wants the terms of its HBOS takeover renegotiated.
It wants to secure the buyout for a smaller fee, given that HBOS - owner of the Halifax - is being forced by the government to raise as much as £12bn.
A £12.2bn deal was agreed last month but the value of HBOS shares has since plunged and the extent of the recapitalisation highlights its weakness.
Both companies insisted on Sunday evening the deal is "still on" but HBOS shareholders are expected to do less well.
Under pressure
On top of the cash to be raised by HBOS, Mr Peston said RBS is likely to get in the region of £20bn and Lloyds TSB about £5bn.
Barclays was under pressure from the Treasury, Bank of England and Financial Services authority to raise up to £8bn, he added.
The investment is part of the £500bn plan to rescue Britain's banks which was announced last week.
The government is not expected to insist on having its own appointees on the boards of the banks, although other strings are likely to be attached.
A key aspect of the announcements will be what the government requires the banks to do in return for the cash.
What a sorry end to Britain's longest ever period of unbroken economic growth
Robert Peston, BBC business editor
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These could involve curbing executive pay and resuming normal lending to individuals and small businesses.
The government has said that it will negotiate terms individually with each bank that participates in the scheme.
"What we're doing now is talking with all of the banks about how we implement the programme," Yvette Cooper, chief secretary to the Treasury, told BBC1's The Andrew Marr Show.
"We'll set out the sort of strings that will be attached on a case-by-case basis," she added.
"What we're doing over the weekend is looking at specifics," Alistair Darling, chancellor of the exchequer, told the BBC in Washington after talks with President Bush and other G7 finance ministers on Saturday.
"We'll be making an announcement at the beginning of the week," he added.
Voting rights
The chief executive of RBS, Sir Fred Goodwin, is expected to resign to be replaced by Stephen Hester, the former finance director of Abbey who is currently chief executive of British Land.
Earlier in the year, RBS raised £12bn from its shareholders, which is now more than the bank is worth on the stock exchange.
Banks trying to raise new capital as part of the scheme may choose to approach their own shareholders again instead of taking part of the government's £50bn.
If they go to their existing shareholders for funding, the government has said it will underwrite the issues, which means that if all of the shares on offer are not sold then it will step in and buy them.
That means that the government could end up owning large stakes in the banks and having extensive voting rights.
Hefty falls
This would be different to the preference shares that the government would get for additional capital.
The difference is that normal shares carry voting rights while preference shares do not, but preference shareholders, as the name suggests, get access to any money that a company makes before the normal shareholders.
If the agreements are reached ahead of trading on Monday morning, it will be just another factor for investors to take into account following the huge falls on stock markets last week.
The FTSE 100 in London fell 21.1% during the week, its worst weekly fall since the crash of 1987.
The Dow Jones in New York fell 18% in the week while the Dax in Frankfurt fell 21.6%.