The Metropolitan Police failed to challenge a claim from Mohamed Al Fayed that he was too ill to respond to a sexual assault allegation, according to an official complaint.

An American woman, Pelham Spong, reported to officers in 2017 that the tycoon had assaulted her a decade before, but the investigation was shut down with police saying they were “unable to obtain an account from the suspect owing to his poor state of health”.

But in a complaint to the UK’s police watchdog, shared with BBC News, Ms Spong’s lawyers say police should have been more thorough in checking the medical evidence provided to them.

The Met said its review of allegations relating to Mohamed Al Fayed remained ongoing and would share its findings as soon as possible.

The complaint said this police failure reflects an “apathy towards victims” or an “institutional desire to insulate Mr Al Fayed from prosecution”.

The BBC has contacted Al Fayed’s estate for comment.

Ms Spong is being represented by the high profile US lawyer, Sigrid McCawley who led legal actions against Jeffrey Epstein – who died in a New York prison cell as he awaited trial on sex trafficking charges.

“This has gone on too long,” Ms McCawley said. “Too many survivors were victims of Fayed and they reported to police.

“They got zero protection. That’s appalling and it has to stop.”

Ms Spong applied for a job as a PA to Al Fayed in 2008, while living in Paris, aged 23.

She told police later that while in London for interviews, Al Fayed grabbed and kissed her, making clear that sex with the boss was a requirement of the role.

The company also required her to have an intimate medical examination, the results of which, she says, were passed to Al Fayed, who appeared to know she had been diagnosed with a minor infection.

She described what had happened in emails shortly afterwards, to friends and a recruitment consultant, but was too scared of Al Fayed’s power to report him.

Ms Spong finally felt able to come forward nine years later and a Metropolitan Police investigation began.

In June 2018 she was emailed by a detective to say they had been provided with expert evidence about Al Fayed, which would “have an impact” on the investigation.

​​Thirteen days later a more senior officer said the case would be closed, partly because police had been unable to obtain the businessman’s response to the allegations, due to his health.

The Met said the case couldn’t be referred to prosecutors because there wasn’t enough evidence.

Ms Spong’s complaint to the Independent Office for Police Conduct (IOPC) concludes the decision to terminate the investigation was “premature and flawed”.

The complaint said: “The police… ought to have been more thorough in assessing the substance and veracity” of the medical evidence provided by Al Fayed.

Al Fayed’s son Omar recently told the Mail On Sunday his father had pretended to suffer from dementia so he could evade prosecution for sexual crimes.

Aging suspects in historical abuse cases have been a common challenge for other police forces. However three years before the Al Fayed investigation ended, a disgraced Church of England Bishop, Peter Ball, was successfully prosecuted despite being in his 80s.

The same year an attempt was made to prosecute the Labour peer Lord Janner, despite four doctors agreeing he was suffering from dementia. He died before a trial could take place.

The Met also told Ms Spong that due to the “historic nature of this allegation” no medical evidence, telephone, CCTV, forensics or eyewitness accounts could be gathered”.

However she says she had given them a file of emails, letters and medical records from the application process, which she has also shared with the BBC.

These reveal the names of employees with whom she came in contact, including two doctors involved in the medical examination she was told she had to undergo.

Her IOPC complaint alleges the police failed to obtain formal statements from the doctors, a recruiter who suggested Ms Spong for the job, and other Harrods staff who might have been able to corroborate her claims.

Ms Spong’s lawyers also believe police asked the wrong company for records about her job application – approaching the firm managing the apartment block where she stayed in London, rather than Harrods itself.

The complaint concludes: “These investigative failures, particularly when viewed alongside the now disclosed prior and concurrent accounts from other women and girls alleging similar misconduct by Mr Al Fayed, suggest a concerning pattern of systemic inaction by the Met.”

Ms Spong said she had been told by the police that if more women made allegations against Al Fayed they could continue to investigate.

But an attempt to reopen the case in 2021 stalled within months.

The Met has confirmed that it was aware of 21 allegations against Al Fayed before the BBC broadcast its documentary last year.

Ms Spong said: “More women did, in fact, come forward to tell their stories of abuse to the Met, and others had before me, and it didn’t make any difference. The Met did nothing.”

Her lawyer Ms McCawley asked: “Who were the decision makers who allowed Fayed to get a complete pass here?”

“It’s beyond unacceptable. They wouldn’t do that with any other suspect – they would have been prosecuted.”

Ms Spong and her lawyers hope the IOPC complaint will be the start of a legal campaign by US victims for a wider investigation into the response to the Al Fayed abuse scandal.

Ms McCawley’s battle against Epstein led to a US Department of Justice investigation “of those who did not do their duty,” she said.

She described Ms Spong’s complaint as a “little jab at the Met”, but “part of a much larger and significant event”.

The IOPC can either reject the complaint, hold its own investigation, or pass the case to the Met for investigation overseen by the watchdog.

It can recommend police officers face misconduct proceedings or prosecution.

The Met added it had transformed the way it investigated sexual offences, putting victims at the heart of its response.

Its review of previous Al Fayed investigations is looking for evidence of misconduct or corruption among officers.

The Met is also investigating people who may have enabled Al Fayed’s abusive behaviour.