Computer problems could occur up to a year before the ''millennium time bomb'' of January 1 2000 and for some time after, industry has been warned.

The Health and Safety Executive said yesterday that if firms were not taking action by the end of this year they might face court proceedings and possibly fines.

Some systems controlling fire alarms, security and lifts may fail as early as January 1 1999, because they used a row of nines to show the end of a file. Other possible failure dates include February 29 2000, since many companies may not anticipate that 2000 is a leap year.

Publishing a free guide for firms on how to cope with the date change, Mr Clive Norris, director of safety policy, said: ''Until the end of this year HSE inspectors will be working with companies to help them get their computers working correctly.

''After that we will be taking safety very seriously and we will start considering enforcement action against those companies that break regulations.''