Thomas Markle could face up to 12 years behind bars in a Philippines prison if he is found guilty of child sex offences.
Authorities have today begun trawling through a trove of child abuse images that allegedly belong to Meghan's 82-year-old estranged father.
Philippines interior minister Jonvic Remulla said the forensics data is expected to be completed in around a week, but 'right now all signs point to a possible sex offender of the grossest kind'. Mr Markle denies the allegations.
Police will then decide whether to formally charge Mr Markle, who is now living in a rehabilitation centre in Florida after returning to the US in May to continue his medical treatment for his leg amputation.
The US has an extradition treaty with the Philippines, which means Mr Markle could be sent there to face a trial should the authorities charge him.
A person convicted of accessing child abuse images faces between 10 and 12 years in prison under the Philippines' Anti-Online Sexual Abuse or Exploitation of Children (OSAEC) and Anti-Child Sexual Abuse of Exploitation Materials (CSAEM) Act 2022.
It comes as the Metropolitan Police faces questions over why it did not alert Mr Markle to the FBI after it was sent a letter which contained 'a number of claims about alleged offending outside the UK' in 2019.
Jim Gamble, an international campaigner against child sexual abuse, said the Met had a responsibility to share this information - and could have left children with an 'extended exposure' to possible abuse over the last seven years.
Thomas Markle is pictured with his daughter, Meghan Markle, in 2011
Exclusive images taken by the Daily Mail show the moment Mr Markle, 82, was given a letter from Meghan cutting him out of his grandchildren's lives
He told BBC Radio 4's Today programme: 'If you get information that comes to you about someone from a foreign jurisdiction who represents a threat to children, there's a well-worn path and you'd expect a UK police force to share that information.
'I would have expected the Metropolitan Police either to have gone to the FBI Legat, the legal attaché in the embassy here, to say, "look, this isn't proven – it's an allegation. You might want to look at it because in America you may have more information to add to this, so you can see whether you can corroborate it".
'But ultimately, it also should have gone to the National Crime Agency. Whilst it seems simple, there is a complex network whereby you can share information, and you should share information.'
The letter sent to the Met Police in 2019 is understood to have been written by Mr Markle's first wife, Roslyn Loveless, who died two years ago.
The seven-page letter, seen by The Sun, details a conversation which Ms Loveless claims to have had with the Duchess of Sussex's father.
She reportedly wrote: 'I questioned Thomas Sr. He denied accusation but stated that he went to the Philippines and Thailand because 12-year-olds are legal there.'
Ms Loveless's letter was addressed to Scotland Yard's Fixated Threat Assessment Centre, which analyses intelligence about threats to the Royal Family. It is said to have accused Mr Markle of being a threat to his daughter and her husband, Prince Harry.
The information was reportedly passed on to the Sussexes, though the Met Police did not investigate the allegations made by Mr Markle's ex-wife because they occurred outside of Britain.
They also admitted that 'the details of the allegations in the letter were not shared with other law enforcement agencies'.
An investigation was launched into Mr Markle after his son, Thomas Markle Jr, alerted Philippine National Police to his father's reported stash at his former home in Cebu.
The FBI has said it is aware of the allegations and would provide support to the Philippines where appropriate. It added that 'any related allegations of federal violations of US law' would also be investigated.
A spokeswoman for No10 said it was a matter for police, but 'they are extremely distressing allegations'.
Mr Markle's lawyers could in theory attempt to block an extradition due to his old age and ill-health. He told the Mail that he has also been diagnosed with dementia.
It comes as exclusive images taken by the Daily Mail show the moment Mr Markle, 82, was given a letter from Meghan cutting him out of his grandchildren's lives.
It was delivered while he was in hospital in December, hooked up to a drip after having a leg amputated.
The explosive message revealed Meghan 'knew her father had abused young girls', and that he would never meet his grandchildren, Archie, seven, and Lilibet, five.
Yesterday, Mr Remulla, the Filipino interior minister, said: 'The Philippine National Police, upon the reports of the son, inspected the former home of a certain Mr Thomas Markle. Found were a trove of child pornography materials as well as a laptop.'
He said the data on the laptop found among Mr Markle's possessions was being analysed 'to determine the contents and come up with a definitive picture'.
He said the country planned to take 'appropriate legal actions' if sufficient evidence was found.
Mr Remulla told The Guardian: 'In these cases where family disputes are mixed up, we have to consider all the angles. Right now all signs point to a possible sex offender of the grossest kind. We want to be sure before we release the findings. The forensics data will be complete in a week.'
Last night, when asked for a response to the interior minister's claim that he may be a 'sex offender of the grossest kind', Mr Markle said: 'I am not. I am innocent. I never did anything in the Philippines.' Mr Markle has told the Mail his computers had not been in his possession since he left Mexico with his son in 2025 and moved to the Philippines.
It is the latest revelation of criminality levelled at Mr Markle after it was revealed yesterday that Meghan had accused him of child abuse in her letter last year.
Meghan and her father in an undated photo
A newly uncovered letter allegedly sent by Roslyn Loveless (pictured in 2016) - his former wife of nine years - claims that Mr Markle admitted he travelled to the Far East to have sex with young girls
Captured by the Mail at the time, the video showing the letter being delivered was filmed as Mr Markle was in hospital in the Philippine city of Cebu.
The retired Hollywood lighting expert was recovering after having his left leg amputated below the knee due to a blood clot.
Mr Markle did not disclose the contents at the time.
He left the Philippines in May to stay in a rehab centre in Florida, leaving his possessions in Cebu with his son, Thomas Jr, who had been his carer.
The Sun reported that Thomas Jr, 60, found 'hundreds, if not thousands' of child-sex images in four boxes, and had reported his father to Filipino detectives and the FBI in the US, which are both investigating.
One 35mm photograph reportedly shows a bearded man resembling Mr Markle having sex with a young Asian girl – although he has said in response he has 'never been in a photograph like that'.
Thomas Jr said: 'When I found this material I was horrified and I had no option but to report my dad. I have supported, cared for him and helped him for years, but that stops now. I won't speak to my father ever again unless I'm called to give evidence against him.'
He later said: 'I'm so, so sorry Meghan. 'I now know I have been protecting the wrong person for the past nine years. Having seen what I've seen, I believe the man I've been defending and caring for is a monster.'
After his revelation, Meghan said she had learned of child sex allegations in 2019 after being contacted by the Met.
She said she was assured the 'troubling and disturbing' allegations were being investigated and was advised that speaking out could jeopardise any legal case.
But the Met has now admitted failing to pass on the details of the 'alleged offending outside the UK' to other law enforcement agencies, presumably those in the US, Mexico and the Philippines where Mr Markle has lived.
The force is considering whether to report itself to the regulator for its failure to do so.
It is unclear why the letter was sent to London with allegations it claimed related to 'offending outside the United Kingdom'.
In an interview with The Mail on Sunday, Mr Markle denied all the allegations, saying he would 'do whatever it takes' to clear his name. He confessed to paying for sex in the Philippines, but added: 'I have never had sex with anyone under the age of 18.'
He said: 'I have always dated age-appropriate women.'
He admitted that when he was single he went to the Philippines at least twice and 'slept with prostitutes', adding: 'I like Asian women, but that is not a crime.'
He said he would willingly speak to police and believes any child-abuse images found on his computer were 'planted' to destroy his reputation. He said Meghan 'never said a word' for seven years about the Met allegations, and then 'cut him off'.
Thomas Jr's sister Samantha said: 'Thomas Jr had possession of those boxes with Dad's computers and phones. They were in storage places which God knows how many people had access to. I believe this is a set-up.'
Meghan has spoken of her 'deep distress' at the allegations, that were 'more sickening than one could ever imagine'.
She added: 'My thoughts are with any children who may have been harmed.'