Three judges headed by Lord Phillips, the Lord Chief Justice, have reserved judgment in the case and will give a written ruling at a later unspecified date.

At London's Appeal Court last week, Balfour Beatty argued among other things that it was not given credit for pleading guilty and that the fine was excessive.

Opening the case last Tuesday, Jonathan Caplan QC, counsel for Balfour Beatty, told the Lord Chief Justice sitting with Mr Justice Nelson and Mr Justice Silber some may think the company was behaving irresponsibly in challenging the fine.

Four people died and 102 were injured when the train de-railed on October 17, 2000.

"Inevitably it may be that some will perceive large companies to be irresponsible if they seek to contest a financial penalty in the wake of a major accident," said Mr Caplan.

However, he said that after the trial judge who imposed the fine had ordered the jury to find the company not guilty of manslaughter it had immediately pleaded guilty to the other charge involving a breach of health and safety regulations.

Mr Caplan said: "We say as a matter of sentencing principle the corporate defendant (Balfour Beatty) should have received a discount for its plea of guilty."

He said that "for a number of reasons" the fine of £10m was "excessive" in the circumstances of the case.

A third ground of appeal was that the judge had been wrong in his assessment of the firm's culpability.

"We have it in mind that his assessment of Balfour Beatty's culpability was somewhere between two and three times that of Railtrack," he said.

"We suggest that the judge was too severe in his assessment of Balfour Beatty's culpability."

The fine was imposed in October last year by Mr Justice Mackay who described what had happened as "one of the worst examples of sustained industrial negligence in a high-risk industry" that he had ever seen.