A British investigative journalist who is facing an arrest warrant in Malaysia over her reports on alleged high-level corruption has been given police protection in London after being followed and photographed in Hyde Park.

Clare Rewcastle Brown, the sister-in-law of former Prime Minister Gordon Brown, has been accused of “activity detrimental to parliamentary democracy” after publishing documents on her blog Sarawak Report detailing how nearly $700m was paid into the personal bank accounts of Malaysian Prime Minister Najib Razak. Officials in Kuala Lumpur have said the money came from an unnamed Arab donor and was for political not personal purposes.

Sarawak Report also alleged that Malaysian Attorney General, Abdul Gani Patail, was preparing an arrest warrant for the Mr Najib just before Mr Patail was dramatically sacked last month. The Royal Malaysia Police this week announced it had obtained an arrest warrant for Ms Rewcastle Brown and would be applying to have her placed on Interpol’s Red Notice list.

In an interview with The Independent, she described the warrant as “ridiculous” and said the tactic was designed to frighten her sources. “It’s not something they could execute against me. They have charged me under laws that don’t exist in the UK or any other normal democratic country,” she said. “What they have said is that I have printed material that has caused concern in the minds of the public and that is a crime, apparently.”

Malaysian Prime Minister Najib Razak (EPA)

She revealed that she had been subjected to sinister surveillance operations in London where she lives and had sought support from the Metropolitan Police. “I have had to put in police reports that I have been stalked and followed.”

Last month she was staked out and photographed having tea at the fashionable Magazine Restaurant at the Sackler Gallery, alongside the Serpentine in Hyde Park, while meeting a former Malaysian official who was on holiday in the UK.

“I had my back to the big glass window and he kept looking over my shoulder and getting nervous and he said ‘You do know you are being followed?’”

A “Chinese-Malaysian” looking man then appeared outside the window “very obviously photographing us” while “pretending to be photographing a bunch of people who had just left the restaurant”, she said. “I got up, went out and confronted him and he ran away.”

The following day details of the encounter appeared on the Internet, accusing the man of being Rewcastle Brown’s secret source and giving his full name and former title, which the blogger said she was not previously aware of. He was arrested on his return to Malaysia.

She reported the matter to Scotland Yard, which confirmed it had received a complaint. “They have put a detail on my house because we have had men sitting in cars, idling. It’s absurd.”

She also fears her emails have been hacked. “[Almost] everybody that has been in touch with me has been arrested.”

Sarawak Report was blocked in Malaysia two weeks ago, purportedly on the basis of a “confession” by Lester Melanyi, a former volunteer for Rewcastle Brown’s radio station Radio Free Sarawak. Melanyi made a video in which he claimed that 90 per cent of documentary evidence used by Rewcastle Brown and her team was forged. He alleged that it was faked by a British forger and “web designer” who he identified as James Steward Stephen. Rewcastle Brown, who described Melanyi as a “fantasist”, promptly pointed out that the name was that of the late Hollywood film star James Stewart and the picture Melanyi used of the “forger” was in fact a photo lifted from the internet of an innocent British bus company executive, based in Norwich.

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Rewcastle Brown, who was born in Sarawak, previously used her blog to expose the deforestation of the Borneo rainforest but broadened its remit as she uncovered evidence that corruption was the cause of much of the destruction. She has reported extensively on how Malaysia has spent huge amounts of money with the Western media to promote itself as a modern democracy and environmental tourist destination. Earlier this year Sarawak Report began reporting on money missing from Malaysia’s debt-laden state fund 1MDB.

Her blogging has meant she has not been able to return to Sarawak and she said it would not be wise for her to go to Malaysia while Mr Najib was in power. “Numerous civil rights activists and free thinkers have been arrested without reason and harassed. The country’s most popular cartoonist is facing 43 years in prison on sedition charges. I’m not going to feel sorry for myself - things are much worse for people over there,” she said.