The deal is £500bn - that is a five with eleven zeros after it, that is one trillion US dollars.

That is the size of the colossal rescue package which, combined with an interest rate cut, is enough to take your breath away. But is it enough to blow out a financial hurricane?

There are three strands to the unprecedented rescue package that the Chancellor told the Commons might not be enough to beat the credit crunch.

Fresh capital
First, the part-nationalisation of the British high street banks. The government is offering £25bn as a first half of a tranche of fresh capital to seven of the big banks and one building society.

The money is being offered in return for the government taking a stake in the banks in the form of a preferential share - effectively, semi-nationalisation.

There will be no seats on the board, no direct governmental direction, in return for the money, which left some left-wingers such as George Galloway MP staggered.

But there will be strings attached to the offer, the Prime Minister made clear at Question Time in the Commons. There will be curbs on the bonus culture for bank executives and guarantees that credit lines will be kept open for small companies suffering.

Glasgow South-West MP Ian Davidson, who met the Chancellor, Alistair Darling, immediately after his Commons statement, said Mr Darling wanted to hear about any situation where banks were not being as supportive and understanding as they should be to businesses and people facing borrowing difficulties.

A further £25bn is being held back to see what effect the first tranche of re-capitalisation has.

The shares may be a good deal for the taxpayer as they could be sold in good times. "Unlike America, where the bad assets have been taken on by the taxpayer, we are putting money into the system and we will get it back," said Mr Darling.

Well, maybe. A stake of up to £50bn in the top UK banks works out at about £820 for every man, woman and child in the UK and it could all be potentially at risk.

Guarantees
The second strand is a gigantic underwriting guarantee of £250bn that will allow more inter-bank lending. A fee will be charged for the service. Providing no bank goes bust, this money will not be called on but if the bottom falls out of the barrel and the whole system collapses, it would be lost. If matters reach that stage, £250bn will not seem a large amount.

While the taxpayer is exposed, this money is expected to be paid back and economists said it was likely to have no impact on the public finances as it should be classed as a contingent liability which would only come into play if a bank defaulted on its commitment.

Liquidity
Add to that a third element of £200bn more being pumped in to the banking system in short-term loans under the Special Liquidity Scheme and half a trillion pounds of taxpayers money is at play in the rescue package.

The Special Liquidity Scheme is designed to help keep the financial system working from day to day. It will allow risky assets to be swapped for Treasury bonds and increase trust between banks There is £100bn of government money in the scheme and this is now doubled. Some media, the BBC notably, are not including the first £100bn in the running total of public money in the plan. Most newspapers, including this one, are calling it a £500bn rescue package.

So, with potentially half a trillion pounds in play in an effort to get the money markets going, it is fair to ask whether this is going to work at all? The plans have been welcomed as a comprehensive approach to the problem, but at this stage it is too early to say. There is no plan B - this simply has to work.

Mr Darling took the step of guaranteeing the savings of all British depositors in Icelandic banks that have gone belly-up and taken the country to the brink of economic extinction. It was a bullish move, backed by legal threats, that proves the government does not want a penny of British depositors' money, from Northern Rock or the north Atlantic, to be lost in this crisis.

It is all going to make for an eye watering Pre-Budget Report in November with some experts warning that the deal will take UK's net borrowing requirement well above £100bn this year - almost three times official estimates.

This in turn will affect government finances already reeling from an economic slowdown. So it's tax rises or spending cuts for the next few years.

Interest rates
The other element of the deal, which the government claims it had nothing to do with but was co-ordinated worldwide, is the half percentage point cut in interest rates in Britain, Canada, the US, the eurozone and, for the first time, China too.

The half percentage point interest cut will mean a saving of £47 a month on a £150,000 mortgage if the reduction is passed on in full by lenders.

Economists said there would be more reductions to come but the rate at which banks lend to each other is higher than the base rate so if the perhaps not all mortgage payers will benefit.

The bank had kept rates on hold at 5% since April as politicians worried about soaring oil, food and energy costs. Inflation reached 4.7% in August, more than double the official 2% target.

But the monetary policy committee of the Bank of England thinks that the inflation worries have diminished while the "recent intensification" of the financial crisis had "augmented the downside risks to growth" - bank-speak for "We're heading for a recession".

That's what kept US and UK markets falling yesterday and there will be more ups and downs before we see whether the five and eleven zeros have any effect.

Explained
Tier 1 capital - The core measurement of a bank's financial strength. It consists of the types of financial capital considered the most reliable and liquid.
Liquidity - The extent to which a security is easily tradeable. Your current account has more liquidity than your house, for example.
Preference shares - Shares in a company which give their holders an entitlement to a fixed dividend but which do not usually carry voting rights.
PIBS - Permanent Interest Bearing Shares are fixed interest securities issued by a building society. They offer a set income paid twice yearly.
Convertible Preferred Shares - Corporate fixed-income securities which investors can choose to turn into a certain number of shares of the company's common stock after a period of time. The fixed-income component offers a steady income stream.