The Metropolitan Police has admitted it did not pass a letter detailing claims of alleged offending outside the UK by the Duchess of Sussex’s father Thomas Markle with other law enforcement agencies.

Authorities in the Philippines are currently investigating allegations that Meghan’s estranged father kept a hoard of child sex abuse images at his former home there – claims he denies and has called a “bunch of lies”.

On Friday, the duchess said a letter, sent to the Metropolitan Police and Royalty and Specialist Protection in 2018, containing “disturbing allegations” about her father was shared with her and she was “given assurances that these were being investigated”.

But in an astonishing admission on Saturday, the force said it had failed to pass those claims on to other relevant agencies.

The Met said it received a letter in 2019 – the year after Meghan said she saw made aware of it – about a “number of claims” relating to Mr Markle and it was now “reviewing it’s handling” of the matter.

In a statement, Scotland Yard said: “Following a thorough review of Met Police systems and records, we have confirmed that in January 2019, we received a letter containing a number of claims about alleged offending outside the United Kingdom. It was sent to the MPS (Metropolitan Police Service) Protection Command to raise concerns in relation to the security of the Duchess of Sussex.

“The letter was reviewed and a decision was made that it should be passed to the office of the Duke and Duchess of Sussex for their awareness. The details of the allegations in the letter were not shared with other law enforcement agencies.

“The MPS is reviewing the handling of this matter in 2019 and considering whether a referral to the IOPC [police watchdog] is necessary to review our approach.”

The revelation comes after Meghan’s half-brother, Thomas Markle Jr, told he had found “hundreds” of child sex images on computers and a cellphone, which were left behind at his father’s home on Cebu when he moved from the Philippines earlier this year.

Mr Markle Sr was forced to return to the US after suffering a stroke and a blood clot, which led to the amputation of his left leg and he is reportedly now living in a rehab centre in Florida, where he is learning to walk again.

Meghan “reached out” to him in the aftermath of the operation, a spokesperson for the duchess said, and she was also said to have tried to do so previously.

She became estranged from her former TV lighting director father in the run-up to her 2018 wedding to Prince Harry after he was caught staging paparazzi photographs.

Mr Markle Jnr said he submitted a police statement in the Philippines, telling the newspaper he was “horrified” by what he found, which gave him “no option” but to report his father.

“I won’t speak to my father ever again unless I’m called to give evidence against him”, he said.

He is said to have reported his discovery to the FBI Hotline and to the state police in Pennsylvania, as well as the US-based National Centre for Exploited and Missing Children in July.

Nicholas Ty, undersecretary for the Philippines Department of Justice, confirmed on Saturday that an investigation was underway in the country.

“Our Anti-Trafficking and Online Sexual Abuse and Exploitation of Children taskforce in Cebu is currently investigating the matter,” he told ITV News.

Mr Markle Sr has denied the accusations and said he believed his son was “trying to destroy” him.

He said: “I’m shocked, I’m hurt and I’m very upset that my son is making these accusations against me. I could never do what I’m being accused of. It’s the worst thing anyone could accuse me of.

“This is bulls***. It’s just a bunch of lies. It’s sick. I have no idea why Tom is trying to destroy me with these lies.”