In sentencing the two companies, Mr Justice Mackay described Balfour Beatty's breaches of the Health and Safety Act as 'one of the worst examples of sustained industrial negligence'.
Balfour Beatty made a pre-profit of £150 million in the year ending December 31, 2004.
Network Rail was convicted of breaching safety rules
last month and at the same time Balfour Beatty pleaded guilty to similar charges.
Four people died and 102 were injured when the King's Cross to
Leeds train came off the tracks at 115mph on October 17 2000.
The prosecution maintained the derailment was an accident waiting
to happen and it occurred because of a cavalier approach to safety.
In evidence, some maintenance and track inspection practices were
described as a Fred Karno circus and a shambles.
The rail which broke - causing the train to fly off the track - had disintegrated.
Defective monitoring meant it had been left virtually uninspected in the months before the crash.
The four, who were working for track maintenance firm Balfour Beatty, had all denied the charges.
They were Stephen Huxley, managing director of Balfour Beatty Rail Maintenance until August 2000, Kenneth Hedley, a track engineer, Vernon Bullen, King's Cross area maintenance engineer, and Keith Hughes, an acting track engineer.
Richard Lissack QC said the prosecution did not intend to press for a trial of the four, on the wishes of the families of those who died in the crash.