Gordon Brown's activist sister-in-law Clare Rewcastle Brown denied entry to Malaysian state

The activist sister-in-law of former British Prime Minister Gordon Brown was refused entry to the Malaysian state of Sarawak yesterday, a place where she has spear-headed a campaign against state corruption and deforestation.

Clare Rewcastle Brown, an investigative journalist and activist, runs the Sarawak Report blog and Radio Free Sarawak, media outlets that are fiercely critical of Sarawak's chief minister, Taib Mahmud.

She arrived at the Kuching International Airport from Singapore at 1.15pm on Wednesday, where immigration officials told her she had been placed on a "not to land" list.

She was later brought to a confinement room at the airport before being put on a plane back to Singapore.

In a video statement on YouTube Ms Rewcastle Brown said she had flown to Sarawak's capital Kuching to meet lawyers over a civil suit filed against her there.

She accused Malaysian authorities of barring her so that she could not defend herself against "a transnational corporation that is on the British and European stock exchanges," and by powerful figures within Sarawak politics, although she refused to give further details about the case.

The spat emerged as the Malaysian Prime Minister Najib Razak, makes an official visit to London to meet Prime Minister David Cameron.

Mr Mahmud has ruled Sarawak - a large state on Borneo island of 2.5 million people and one of Malaysia's poorest states - since 1981, during which time activists and environmentalists have accused him and his family of enriching themselves at the expense of its people.

Under his tenure, Sarawak has experienced the highest rates of logging in the world, with just 5 per cent of its rainforests remaining intact.

"He's the tail that wags the dog in Malaysia at the moment, and he runs the state [of Sarawak] as a private business," Rewcastle Brown said," if it wasn't for the votes that he is able to deliver through his strongman tactics, Najib wouldn't be in power."

An investigation by the Malaysian Anti-Corruption Commission (MACC) was launched two years ago into Mr Mahmud's regime, although anti-corruption groups say it is being deliberately slowed down by the government.

"The MACC seem either powerless or are recalcitrant in bringing some of the serious allegations against Taib [Mahmud] to a satisfactory conclusion. It appears clear to all that he is being protected by the powers that be," said Ambiga Sreenevasan, co-chairperson of Malaysia's Coalition for Clean and Fair Elections, also known as Bersih, adding that the proceedings against Rewcastle Brown were "tainted".

Corruption is endemic in Malaysia: it was last year cited as one of the world's worst offenders by Transparency International for paying bribes, with international corruption watchdog Global Financial Integrity ranking it as the world's third largest source of illicit financial flows - an estimated US$285bn (£187bn) in capital flight in the decade up to 2010.

Rewcastle Brown's campaigns have frequently got her into hot water with the Malaysian authorities. She has received death threats and her media outlets have been blacklisted since 2011.