A high-profile Hong Kong pro-democracy activist living in the UK has been the target of a campaign of harassment involving letters containing fake, sexually explicit images of her sent from China to her neighbours.

Carmen Lau, 30, who fled Hong Kong four years ago, told the BBC she was "shocked" as the letters, delivered to addresses in Maidenhead, included her name and images made to look like she was either naked or in underwear and offering sexual services.

"The letters had a couple of very unpleasant images, AI-generated or photo-shopped, where they put my face on those images, portraying me as a sex worker," she said.

The existence of the letters was first reported by the Guardian.

The first she knew about the letters was when the local MP, Liberal Democrat Joshua Reynolds, called her to say he had been alerted to them by some of his constituents who had received them.

Ms Lau had sought sanctuary in the UK in 2021 after opposition politicians and pro-democracy activists in Hong Kong began being arrested following the imposition of a controversial new National Security Law.

While in the UK, she has frequently criticised China's Communist leadership and has spoken out about China's controversial plans to build a "mega embassy" in London, warning that it could become a base for trans-national repression of China's critics abroad.

Last year, up to a dozen of the same neighbours in Berkshire had received letters sent from Hong Kong, and purporting to come from the police, offering a bounty payment of £95,000 to anyone who would hand Ms Lau over to the Chinese embassy in London.

The new letters were sent last month from the Chinese territory of Macau, close to Hong Kong.

"I was quite shocked because last time it wasn't explicit and so unpleasant to see," Ms Lau said.

"When I was in Hong Kong, pro-Beijing agents were trained to use gender-based harassment targeting pro-democracy activists," she said.

"But AI technology has enhanced this sort of intimidation. It is beyond just transnational repression - as a woman, it is very worrying."

Reynolds told the BBC that the government needed "to be very clear that this is not acceptable, we cannot have these letters sent to UK residents".

"We need to find out who sent these letters," he said, adding: "Officials in Beijing need to be held accountable."

Reynolds said he had raised the issue with both the Home Office and the Foreign Office.

A government spokesperson said: "The safety and security of Hong Kongers in the United Kingdom is of the utmost importance."

Thames Valley Police, meanwhile, said it was investigating reports of a malicious communications offence involving digitally altered images.

"We are engaging with the victim and, at this time, no arrests have been made," a spokesperson said.

The government has previously insisted that any attempt by a foreign power to intimidate, harass or harm individuals or communities would not be tolerated.

It has said the UK continues to raise concerns about transnational repression directly with the Chinese and Hong Kong authorities, and has publicly condemned the issuing of arrest warrants and bounties by the Hong Kong Police Force.