A £10m fine imposed on engineering firm Balfour Beatty over the Hatfield rail crash was "excessive", defence lawyers have argued in the Court of Appeal.
Balfour Beatty challenged its fine for the Hatfield rail crash
The company admitted breaching the Health and Safety at Work Act after the disaster in October 2000, in which four people died and 102 were injured.
Jonathan Caplan QC argued Balfour Beatty should have received a discount on the fine because it pleaded guilty.
Judgment was reserved on the appeal which followed a trial last October.
Mr Caplan told the Court of Appeal: "Inevitably, some will perceive large companies as irresponsible if they seek to contest a financial penalty in the wake of a major accident.
"We don't believe that is the case here."
He said the company in pleading guilty "recognised that it had failed in its duty and publicly apologised".
The firm registered its complete commitment to learning from what had happened and to playing a full role in ensuring railway safety and maintaining a proper safety culture, he added.
"Nothing I say today is intended to detract from those sentiments," Mr Caplan said.
The crash happened when a broken rail caused the derailment of a London-to-Leeds express train travelling at 117mph.
The faulty rail was spotted 21 months earlier but left unrepaired even though a replacement rail had been delivered and left alongside it for six months.
Balfour Beatty, which was responsible for track maintenance at the time, received a record fine of £10m. Network Rail - formerly Railtrack - was fined £3.5m for breaching health and safety regulations.
The companies were also ordered to pay £300,000 each in costs.
Old Bailey judge Mr Justice Mackay ordered that a verdict of not guilty should be entered on a charge of corporate manslaughter.
He said at the trial the company's failure to abide by safety rules was "one of the worst examples of sustained industrial negligence in a high risk industry I have ever seen".
Until the Hatfield case, the largest fine imposed in the English courts for health and safety failings was £2m on Thames Trains following the 1999 Paddington rail crash.