Harold Macmillan launched premium bonds in 1956

The computer is being introduced to cope with a six-fold increase in bond sales over the last 10 years.

It will also help process an increase in prizes on offer, from 865,000 to one million from September.

The first machine was unveiled in 1957, when the bonds were launched by Harold Macmillan to encourage thrift. About 23 million people now hold bonds.

A HISTORY OF ERNIE How the UK's money-making machine has changed At-a-glance

Sales of the bonds, which have long been popular presents for children, have boomed in recent years as stock markets have collapsed and interest rates have fallen to historic lows.

The value of bonds has increased from �4bn in 1994 to �25bn in 2004.

PREMIUM BOND SELECTION? Ernie generates numbers randomly. These are then matched against bond numbers Statistical calculations allocate numbers to prizes The first bond number that matches the first number produced by Ernie wins the �1m jackpot Ernie is not linked to a network so it cannot be hacked The numbers are checked by the Government Actuary's Department Q&A: Premium Bonds

From September, the odds of winning prizes will shorten from 27,000 to 1 to 24,000 to 1.

One prize of �1m is awarded each month but 90% of prizes are either �50 or �100.

Ernie 4 produces one million winning numbers an hour, three times faster than Ernie 3, 15 times faster than Ernie 2 and 500 times faster than Ernie 1.

National Savings and Investments, which issues the bonds on behalf of the Treasury, says the random behaviour of its oscillator chip means that each single bond has an equal chance of winning a prize.