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Chancellor George Osborne will use next week's Budget to "lock in" Britain's status as a "safe haven" after seeing official figures which reveal that the low cost of long-term interest rates will save the country £20 billion in debt interest over the next five years.

The Treasury estimates this is worth approximately £1,000 per UK household.

The government is to consult over the issuing of so-called "super long" and "perpetual" gilts, or loans, in an effort to take advantage of current low long-term interest rates. Treasury officials say that this is like the country taking out a low rate, fixed-term mortgage.

Some loans would last 100 years - double the length of the longest loan currently. Others could last forever - in other words the government would pay back the interest in perpetuity, but not the principal sum borrowed. The last perpetual loan was taken out to cover the cost of World War I.

The chancellor is accompanying the prime minister on his trip to the United States where he will have meetings with the US Treasury Secretary and the head of the IMF.

Officials travelling with him say that next week's Budget has still not been finalised. There will be another meeting of the coalition's governing "quad" on Friday. The quad is the name given to meetings of the prime minister and chancellor from the Conservative side, and the deputy PM and chief secretary to the Treasury from the Lib Dem side.

One source said "things are still moving around", but insisted that many issues had been resolved. The Treasury has to inform the independent Office for Budgetary Responsibility of its key tax and spending decisions by the end of Friday in order that the OBR can factor them in to its economic forecasts.

The Treasury is expected to spell out the details of its credit easing plan - to underwrite loans for small businesses - next Tuesday on the eve of the Budget.