Lawyers representing jailed former Nigerian oil state governor James Ibori have alleged serious misconduct by Britain’s prosecuting authorities, a London court heard on Monday.

The allegations include that the prosecution team failed to properly disclose information to the defence in relation to alleged corruption by a British police officer involved in the investigation, and that it made misleading statements in court.

Ibori, who was governor of Delta State from 1999 to 2007, is serving a 13-year sentence in a British jail after pleading guilty in 2012 to 10 counts of fraud and money-laundering.

In his heyday, Ibori was a power broker at the heart of the People’s Democratic Party, which was then ruling Africa’s most populous country and top oil producer.

His conviction in Britain was seen as a high point in efforts to fight corruption in Nigeria, an endemic problem there, but also in Britain, the former colonial ruler and a destination of choice for the proceeds of Nigerian graft.

However, Ibori’s conviction on at least one count is now being called into question by his defence team, Judge David Tomlinson told Southwark Crown Court.

Prosecution lawyer Jonathan Kinnear, who took over the case earlier this year after the previous team stood down, said the Crown Prosecution Service (CPS) was conducting a review into whether Ibori’s convictions were sound and expected to conclude it in August.

If the allegations of prosecutorial misconduct were confirmed and one or more of Ibori’s convictions were quashed, it would be a major embarrassment for Britain at a time when it is trying to make a big push in the fight against corruption.

Prime Minister David Cameron hosted a global anti-corruption summit in London last month in which Nigerian President Muhammadu Buhari took part. Days earlier, Cameron was caught on camera calling Nigeria “fantastically corrupt”.

Ibori’s defence team have applied for Judge Tomlinson to permanently halt court proceedings on the confiscation of Ibori’s assets, which have been dragging on for years.

But the judge, having read the defence lawyers’ formal application for a stay, said that it amounted to a challenge on Ibori’s convictions, a matter that should probably be dealt with by the Court of Appeal, a higher court.

“I am being invited to trespass into matters which are beyond my jurisdiction,” he said.

Kinnear told the court the issue of how and when the defence team had disclosed information “in relation to allegations of corruption” to Ibori’s lawyers was being reviewed by the CPS.

The CPS had previously said that initial results of its disclosure review “have found that material exists to support the assertion that a police officer received payment in return for disclosing information about the investigation”.

No ruling was made at the Monday court hearing. Judge Tomlinson adjourned the case until Wednesday.

Ibori did not attend the hearing. He is being held at Huntercombe Prison in Oxfordshire, northwest of London. REUTERS