LONDON (Reuters) - A Nigerian politician who was jailed in Britain for laundering tens of millions of dollars in stolen public funds through British banks and properties lost an appeal against his conviction in London on Wednesday.

FILE PHOTO: James Ibori, former governor of Nigeria's Delta State, speaks after a court hearing outside the Royal Courts of Justice in London, Britain, January 31, 2017. REUTERS/Estelle Shirbon/File Photo

The Court of Appeal’s ruling against James Ibori, a former governor of oil-producing Delta State in southern Nigeria, is a relief for the British authorities at a time when they are trying to stem the flow of dirty money from overseas through London.

Ibori, who in his heyday was one of Nigeria’s richest and most powerful men, pleaded guilty in a London court in 2012 to 10 counts of fraud and money-laundering involving sums amounting to at least 50 million pounds ($66 million).

He received a 13-year jail sentence of which he served half, as is common in the British system, and is now back in Nigeria.

Anti-corruption campaigners had hailed the case as a milestone for Nigeria, where no one of his stature had been successfully prosecuted, and for its former colonial ruler Britain, long seen as too complacent about the proceeds of Nigerian corruption being laundered in the UK.

“(Wednesday’s ruling) sends a clear message to the world that James Ibori, a man who stole millions from the Nigerian government and laundered those proceeds in the UK, has been rightly held to account,” said Ben Wallace, Britain’s minister for security and economic crime.

Ibori owned multi-million-pound homes in Britain, South Africa and United States, including an English country house near the private school where his children were being educated. He also owned a Jaguar and a Bentley and was buying a $20-million private jet at the time of his arrest.

This contrasted sharply with the situation in Delta State, a maze of mangrove creeks criss-crossed by pipelines and plagued by violent conflict over access to oil money, where most people make do without electricity or clean water.

Wallace said that following Wednesday’s ruling, Britain would work with the Nigerian authorities on the repatriation of criminal assets for them to be used for the benefit of the Nigerian people.

“We will pursue this vigorously through the legal process,” he said.

ALLEGED POLICE CORRUPTION

Despite his guilty pleas, Ibori appealed against his conviction alleging that one of the British police officers who investigated him had taken bribes from a private detective in return for inside tips about the probe. The officer denies this.

Ibori also alleged that British prosecutors had covered up the corruption, tainting the judicial process. These allegations had threatened to turn the case into a major embarrassment for Britain.

But three senior appeal judges said the bribery was not proven, and if it had happened, Ibori himself had instigated it as the private detective was working for him.

“As Ibori was instrumental in (the officer’s) corruption, if corruption there was, he cannot, even arguably, rely upon it to escape his convictions,” the ruling said.

Ibori has now resumed political activities in Delta State.

In a statement sent to media after Wednesday’s ruling, he accused the Court of Appeal of being part of the cover-up and said he would take his case to the European Court of Human Rights.

Britain is currently trying to crack down on money-laundering by people involved in corrupt politics or business abroad. Police say about 100 billion pounds of dirty cash moves through or into Britain each year.

The Ibori case, which pre-dated the current crackdown by over a decade, relied on evidence obtained in Britain and Nigeria during several years of close cooperation between the British police and Nigeria’s own anti-corruption force.