Nuclear whistleblowers who try to draw attention to cultural and safety issues face bullying, MPs have warned.

Members of parliament’s public accounts committee have said they are concerned about the way people who raise concerns about culture and safety on nuclear sites are treated.

“There is generally a problem with whistleblowing and a safety culture,” said Rachel Gilmour, a Liberal Democrat MP, when quizzing nuclear bosses on Thursday.

“That relation between bullying and safety within a nuclear context” needs greater examination, Gilmour said, adding that her office was seeking to raise the issue further with regulators.

The Guardian’s Nuclear Leaks investigation has revealed claims of bullying, sexual harassment and drug use at the nuclear waste dump, Sellafield, which could put safety at risk.

Gilmour’s interjection followed a refusal by Euan Hutton, the chief executive of the Sellafield site, to apologise for its treatment of an HR consultant, Alison McDermott, when asked to by Anna Dixon, a Labour MP. Hutton also refused to say whether he considered the cost of the case against McDermott to be a good use of public funds.

Sellafield, in Cumbria, spent about £750,000 in its pursuit of McDermott’s claim that she was wrongfully dismissed after raising concerns of a “toxic culture” at the Sellafield site.

McDermott was found by a judge to have blown the whistle by raising reports of harassment. The judgment was made in 2023, after an appeal over the findings of an employment tribunal.

Still, along with the oversight body the Nuclear Decommissioning Authority (NDA), Sellafield sought to recoup costs of £40,000. A judge reduced these to £5,000. McDermott told the Guardian she intends to appeal against this decision.

Dixon said she was “disappointed” by Hutton’s response. She said it was “critical for a safety culture” that people feel able to speak up.

Hutton acknowledged there had been problems faced by staff but that there had been progress in recent years.

“We’ve had an improvement … [in employment surveys], we’re not complacent, we’ve got a lot to do,” he said. “We have robust processes” for dealing with any safety concerns raised by staff, he added.

Hutton also acknowledged major cybersecurity failings at the site, which were also first revealed by the Guardian.

He said that “as an organisation we let ourselves down”, by failing to meet standards, but he repeated denials that the world’s largest plutonium store had been subject to “successful” cyber-attacks.

Sellafield was ordered to pay nearly £400,000 after pleading guilty to leaving data that could threaten national security exposed for four years.