Drive to save employers' cash threatens confusion.
The problem is that computers read the date by the last two digits, and they may fail unless they are overhauled to recognise the first year of the next century, 00.
The double zero will either mean nothing to the computer chip, or if it is sophisticated enough, it may decide it's 1900.
The "bug" has come about as a direct result of computer programmers trying to save employers' money.
In the early days of computers, when systems were big enough to fill a room, programmers were under acute pressure to save space, because it was expensive.
All sorts of methods were used and one involved cutting back date calculations in programs to just six numbers.
So instead of a database program having to hold 30/05/1961 it was written 30/05/61.
This might not seem like much of a saving but every bit counted when bytes cost thousands of dollars each, since each program could contain millions of dates relating to millions of data records.
The practice caught on and most computer programmers followed the same space-saving tradition even when the cost on space eased as computers became cheaper.
On January 1 2000 all of the old programs which have not been fixed will become completely confused, because to them the date will be 01/01/00, an impossible figure to calculate.
So, who will the Millennium Bug actually affect?
The answer is everybody - all computerised equipment which has not been altered, including household devices controlled by computer chips, could fail.
Nuclear power stations, hospitals, train signals, traffic lights, air traffic control and weapon systems are possibly all at risk.
To a DSS computer which decides it is 1900, a woman born in 1920 would become minus 20 years old - and ineligible for a pension cheque.
In hospitals, computer systems run everything from drips to patients' waiting lists.
Home computers are also vulnerable.
The average model keeps a note of the year in five separate places.
Prime Minister Mr Tony Blair says the bug is a "serious threat to our economic performance," with the possibility of major disruption to essential services such as benefit payments or even emergency services such as hospitals, the fire service and police.
Action 2000 has been set up to alert business and industry to the threat.
Around pounds 97 million of public money - most of it recruiting "bugbusters" - is being spent on the problem and pounds 200 million is being made available to the National Health Service to prepare computer systems.
Business interests are also taking action, with entire industries such as food retailing, represented by the Institute of Grocery Distribution, (IGD) setting up Year 2000 advice services, aimed at medium-sized enterprises with 80 to 300 employees.
The Confederation of British Industry (CBI) has joined forces with several major companies to produce a Millennium Brief - encouraging all companies to make sure their computer chips can cope with the Year 2000 date change.
Supermarket giant Sainsbury's started work on converting computer software in 1995.
It has a budget of pounds 40 million which is being used to produce an inventory of all IT systems, has contacted suppliers to make sure they are checking systems, and has set up a helpline and introduced a testing programme for all equipment.
Car manufacturer Rover has also been getting ready since 1996.
It has created a Millennium programme office to share information and best practice.
It is working with other manufacturers to ensure all Rover cars are Millennium compliant.
And power supplier and distributer Yorkshire Electricity Group started work in 1996 with an emphasis on safety and ensuring a continuity of supply.
There are programme teams in each of the major business areas addressing the impacts and solutions, these are supported by teams of specialists in information technology, engineering, audit, planning and project management.
Britain is working faster than some countries to sort out the problem - but no one will know if we have succeeded until the clock strikes midnight at the end of the century.