The novelist Nina Bawden, whose husband was killed in the Potters Bar train crash, has called for an overhaul of the corporate manslaughter law.
Manslaughter charges against five rail executives were dropped
It comes after Network Rail and Balfour Beatty were fined a total of £13.5m for breaching health and safety regulations over the 2000 Hatfield train crash.
Four people died and 102 were injured when the London to Leeds train was derailed by a cracked section of track.
Ms Bawden told the BBC that justice had "not at all" been done.
Balfour Beatty and five rail executives had also faced charges of corporate manslaughter but were formally cleared by the judge due to lack of evidence.
The case against four Balfour Beatty workers, who were also facing charges over the crash, were dropped this week.
Under existing law, a company can only be convicted of corporate manslaughter if a senior individual in that company is guilty of "gross negligence manslaughter".
In March, the government published a draft bill for consultation over a reform of corporate killing laws and said it was looking for parliamentary time to introduce the legislation.
Nina Bawden, whose husband Austen Kark, a former managing director of the BBC's World Service, was one of seven killed at Potters Bar in 2002, said the current law was inadequate.
"If you are going to make companies, corporations, actually responsible for the safety of other people's lives, then if they fail in their duty, the only thing to prevent them failing in their duty is the fear that they would be put behind bars," she said.
"A fine that they are not going to pay themselves is totally inadequate.
"Fines don't in fact affect the people who were responsible for relaxing the safety regulations. All they will do is be paid by the corporation, and eventually by us, the taxpayer."
Joshua Rozenberg, legal editor of the Daily Telegraph, said the draft reform of the current law had been suggested by the Law Commission as long as 10 years ago.
It recommended a new offence of corporate manslaughter for a killing that would apply if the company as a whole had failed to meet health and safety requirements, he said.
But he said if the bill became law, it still would not mean a prison sentence for those found guilty.
Had the proposed law been in use it would not have sent anyone from Network Rail or Balfour Beatty to jail, unless an individual had been found to be culpable, he added.
"It's only fair to say that even if there were to be a corporate manslaughter law, the only thing you can do to a corporation is to fine it.
"You can't actually send a corporation to prison and you wouldn't be sending its officers to prison, so it wouldn't have any very different effect from the huge fines that we saw yesterday."
In cases of "cumulative negligence", with each individual contributing to the cause, a prison sentence was probably not fair, he said.
"But of course [a fine for manslaughter] would have seemed different, because you would then have had a company condemned for manslaughter, which most people would consider more serious than condemned for health and safety breaches - even though the punishment might have been similar."