(Adds comment from lawyer)

By Paul Simao

JOHANNESBURG, Feb 19 (Reuters) - A British woman working for the human rights organisation Global Witness has been arrested and charged with espionage in Angola, the London-based group said on Monday.

Sarah Wykes, an anti-corruption campaigner who was in Angola to meet representatives of civil organisations, was detained by police on Sunday morning in the oil-rich enclave of Cabinda, Global Witness said.

She appeared in a Cabinda court on Monday after spending a night in jail, Martin Nombo, one of Wykes' lawyers, told Reuters by telephone. He said he and two other lawyers were forced to leave the courtroom during her appearance.

"The prison she's in is in bad shape. There is a lack of hygiene, ventilation and water," Nombo said. "We're still trying to see if we can get her released tonight and pay the ($2,250) bail on Wednesday."

Angolan banks are closed on Tuesday for a national holiday.

Wykes told the BBC after her arrest she was in Cabinda meeting local groups to discuss oil-related "revenue transparency" issues.

Global Witness said there was no evidence for the espionage charge and has demanded her release.

There was no immediate comment from the Angolan government on the case. The British government said on Monday it was aware of Wykes' arrest and was discussing her case with Angolan officials.

"Our consular staff have spoken to her several times and are on their way to Cabinda," a spokeswoman for Britain's Foreign Office in London said.

Angola, sub-Saharan Africa's second largest oil producer after Nigeria, is often accused of having one of the world's most corrupt oil sectors, with large portions of revenue unaccounted for each year.

Angola, however, has refused to bow to Western demands that it make its economy more transparent, turning instead to China for the credit and loans to reconstruct after a devastating 27-year civil war that ended in 2002.

The government in Luanda tends to take a dim view of foreign activists, especially when they are perceived to be meddling in Cabinda, a former Portuguese protectorate that is seen as critical to Angola's economic development.

Separated from the rest of Angola by a small strip of the Democratic Republic of Congo, Cabinda accounts for between 50 percent and 65 percent of the 1.4 million barrels of oil produced each day in the southwestern African nation.

It was incorporated into Angola after independence from Portugal in 1975, a move that triggered a 31-year war with rebels who did not want to fall under the control of the government in Luanda.

An umbrella group of Cabinda rebel factions signed a peace agreement with the government in August. (Additional reporting by Zoe Eisenstein in Johannesburg and Sophie Walker in London)

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