Computer breakdowns stemming from systems failing to recognise today's leap year date are expected to be insignificant.

Although the problem has been identified on a number of software programmes, including Microsoft's Excel, most users are believed to have been alerted, and have managed to "patch" the problem at this stage. Utilities have said they plan to have additional staff on standby, but many said they dealt with the problem as part of their Year 2000 projects.

According to software quality consultant, Mr Patrick O'Beirne, the glitches should be fairly isolated, and even when they do arise may not have a major impact on the user's computing requirements.

"It may impact any programmes dealing with workflow, accounting or ageing calculations, where they will perform calculations including dates from 1900. However, these problems would probably have arisen already for programmes conducting end of month or forward looking reports at the end of January."

In the UK the Government's Action 2000 task force has identified 21 software packages that will not recognise the date, and warned that some problems may not surface until the end of the year when computers try to end the year a day early.

The confusion stems from the Gregorian calendar, which in order to cope with the 365 and a quarter days it takes to go around the sun the calendar added an additional day every four years.

Because it doesn't always amount to exactly a quarter day, every 100 years the day was not added. Some programmers wrote this into their code for the year 2000. However, they did not realise that every 400 years there is a minor adjustment and there should be a leap year at the turn of a century.