Margaret Beckett, Leader of the House of Commons, said that while most public bodies had made great strides in preparing for the 2000 date change, some departments gave serious cause for concern.
With fewer than 300 days to go before the changeover, she revealed that United Kingdom embassies abroad and key Ministry of Defence agencies were not likely to be "millennium compliant" until as late as December.
Mrs Beckett singled out the Foreign Office and the MoD as in need of major improvement as she published the first league tables showing the progress of government departments and agencies.
The minister also attacked police forces for failure to draw up contingency plans should computers and other equipment be crippled by the date change.
In her fifth quarterly statement to Parliament on preparations for the bug, Mrs Beckett announced that more than half of the 46 police forces in England and Wales do not yet have business continuity plans in place.
The cost of tackling the bug within all Whitehall departments stood at pounds 420m, a rise of 2.5 per cent on the previous quarter.
The tables show that more than half of government departments had finished correction work on their computer systems. The worst performers were the Ministry of Defence Procurement Executive, the Defence Evaluation and Research Agency and the Home Office's Forensic Science Service, which are scheduled to be compliant only by December. The RAF is the slowest of the armed services and won't be ready until November. And the Foreign Office and the Royal Navy will not be bug-free until October.
Some agencies, such as the Vehicle Inspection Agency and Ordnance Survey, had slipped behind by up to 18 months from original plans to achieve full compliance.
A Cabinet Office source said some departments would be told they had to "do a damn sight more" to improve performance.Reuse content