The computers that think they are time travellers

Expect chaos from the 'millennium bug' at the turn of the century, warns Charles Arthur

In four years' time, many computers may take a spectacular leap back in time to 1900 - because their internal clocks calculate that that is the year which follows 1999.

The effects could be dramatic, and are so far-reaching that they were debated last night in Parliament. For example, in one of the "nightmare scenarios" people born in 1965 might receive the startling news that though they are only 35 their pensions are available for collection.

The problem would arise if the computer system administering pensions for the Department of Social Security (DSS) contains the programming flaw known as the "Millennium Bug". This common error is caused when data about the year is contracted to a two-digit number.

In that case, the pensions system would calculate someone's age by subtracting their date of birth - recorded as '65' - from the present year, which would be '00', and deciding that the person must be 65 years old.

But yesterday, government departments were unable to give concrete estimates of how much the changes to the programs which make such calculations will cost, or when they would be complete.

The DSS's computer branch, the IT Systems Agency, yesterday admitted that it does not yet know what the full impact will be on the day after 31 December 1999. It does know, however, that many of its thousands of computer systems will be affected.

"We aim to make sure that nobody will be affected," a spokeswoman said. "We are sure that the changes can be made within the normal maintenance and upgrade routines. There is no risk that key benefits systems will fail."

Government departments generally are rapidly running out of time to find and fix the hidden problems in the thousands of computer systems which are date-dependent. The problem is worst on large mainframe systems - such as those used to process benefits and tax payments - but also occurs on personal computers (PCs).

The problem is not limited to government: banks and insurance companies also face big problems. But according to Jacky Olivier, of the computing services company Hoskyns, many managers are not thinking carefully enough about the possible effects. Some, she adds, are "in denial" about the possible effects. "It's an issue for everybody. The only question is, how big is the mountain that they have to climb. For some companies, it could be life-threatening," she said.

Making the change is not simply a matter of resetting the computer's internal clock to 1900 and adding 100 to any subtraction. This could result in benefits being offered on a Sunday, because some payments are triggered by a particular day of the week - and 1 January 1900 was a Monday, whereas 1 January 2000 will be a Saturday.

Ms Olivier provides consultancy and advice to organisations planning for the programming changes. "A big organisation, such as a bank, will have 10,000 different programs containing date information which must be checked," she said.

"That's probably three days' work per program. That's a total of 30,000 work-days - or 115 work-years. The cost of doing that is in the millions. The worst thing is that there's no business benefit from doing it, except that you won't go bust."

The Inland Revenue say that the cost of making the changes will be subsumed into its computing budget. With so many interlocking computer systems - from local government, banks and departments - requiring change, the possibilities for error are huge.

The DSS said that it is concerned, for example, about data arriving from local government about housing benefit. "Any change has to be done in conjunction with the rest of government and associated organisations," a spokesman said.

However, the DSS has been working on the problem only since last year, and could not provide any information about how many people were concerned with the project.