The Bank of England has announced details of a £50bn plan to help prevent the credit crisis causing more damage to the UK banking system and economy.
The plan should make it easier to get a mortgage
Banks will be able to swap potentially risky mortgage debts for secure government bonds to enable them to operate during the credit squeeze.
The BBC's economics editor, Stephanie Flanders, explains the implications:
How does this compare to what other central banks have done?
No central bank has launched a scheme with exactly this design, although it is similar to facilities launched in the past few months by the US Federal Reserve.
The US programmes, including two schemes of $100bn (£50bn) each announced in March, are larger in absolute terms but, relative to the size of the British banking system this plan is much larger than anything any other central bank has attempted.
When will we know whether the operation is working?
Officials say they will not announce how much money has been lent under the programme until the facility is closed in six months' time.
That is because they are trying to prevent there being stigma attached to this programme.
Unlike previous schemes, banks will be able to access it whenever they want, without anyone in the market knowing they have done so.
That means it will be difficult to directly judge the success of the scheme, although it is safe to say it will be considered a failure if the inter-bank lending (Libor) rate stays at a very high level and banks continue to have trouble accessing liquidity.
How much will this cost taxpayers?
In theory, not a penny.
The Treasury has to put up the money for the Bank to provide the government bonds to banks in exchange for their mortgage-backed assets, but officials have designed the scheme so the taxpayer is protected from any fall in the value of those assets (or the mortgages they are based on).
The main safeguard is that they will be exchanging the assets at a discount, below their market value, and the Bank will be able to demand extra collateral from the banks on a daily basis if the market value of the assets goes down further.
Will this make it easier to get a mortgage?
That is the hope - though it would be an indirect effect of the scheme. Since banks will only be able to bring assets based on mortgages created before 2008, this scheme will not directly support new mortgage lending.
But the Bank would hope that having greater liquidity in the money markets would indirectly make things easier for all kinds of borrowers - small businesses, for example - as well as mortgage borrowers.
The idea is that banks will become less reluctant to lend to one another, so they will pay less for the money they borrow on money markets, which hopefully will mean they charge less for the money they lend to all of us.
Do the banks deserve this bailout?
The Bank and the government would not consider this a bailout.
All it is supposed to do is ease the logjam in the money markets. It is not letting banks off the hook for making bad loans.
There has been some discussion in the US and in the UK of the central bank buying mortgage-backed assets outright.
That would be closer to a bailout because banks would be literally getting rid of the assets.
Since this is a swap - a loan - it is less vulnerable to that kind of criticism.
If this scheme boosts confidence in the banking sector and pushes up the bank shares, some will argue that it is supporting bank shareholders. But that's an inevitable consequence of trying to prevent the credit crunch spreading any further to the real economy.
Why is the government doing this now?
The Bank have been thinking about taking more action for 5-6 weeks and discussing it with the big banks.
Things got more serious over the past two weeks, as the rate at which banks lend to each other (the Libor) started going up again, suggesting that the problems in the money markets were not getting any better.
Could a lending programme like this have saved Northern Rock?
Unlike the other schemes the Bank has launched since September, this programme would have been large enough to make a difference to Northern Rock.
However, it is only designed for fundamentally healthy banks.
Bank officials say that if any bank attempted to fund a large part of their balance sheet through this scheme, as Northern Rock would have needed to, they would conclude that bank was in trouble and that the scheme was not appropriate to them.
More broadly, at the time Northern Rock began to have difficulties, there was no suggestion of any central bank launching a scheme of this kind - let alone on this scale.
To do so at that time would have been considered a dramatic vote of no confidence in the entire banking system.