Lawyers for the Nigerian government filed “new and substantive” allegations of fraud with a British court, carrying on a fight against an arbitration award now worth close to $10 billion, a spokesperson for the attorney general said.

The government has been contesting efforts by British Virgin Islands-based Process & Industrial Developments (P&ID) to enforce the award for a failed gas project and is also seeking to overturn the underlying award, the spokesperson said.

The filing has been expected for months, as the window to appeal the award expired and proving fraud or corruption in the foundation of the contract is the only way to overturn it.

“Nigeria’s new filings with the English Court is an act of desperation to try to undo the Court’s sound conclusion that P&ID’s $10 billion award is enforceable,” P&ID said, adding that the award is now worth $10 billion due to interest accrued.

Attorney General Abubakar Malami and other government officials have repeatedly said that an investigation this year by the country’s anti-graft unit had uncovered proof of fraud.

“The challenge argues that the (contract) was procured on the basis of fraud and corruption, while the subsequent arbitral process was riddled with irregularities and deliberately concealed from the rest of the government,” Malami’s spokesperson said in an emailed statement.

The attorney general’s office calculates the total to be roughly $9.7 billion. Details on the evidence uncovered were not available as the spokesman said that court filings and documents are sealed until they are referred to in open court.

Nigeria’s anti-graft unit has already charged a former government lawyer with allegedly taking bribes and charged two Britons with money laundering in relation to the case.

The 2010 deal called for P&ID, which was set up solely for the project, to build a gas processing plant, and for the government to supply it with gas.

It collapsed without any construction taking place, though P&ID said it spent $40 million on a design and feasibility study. P&ID initiated arbitration in 2012, and in 2017, a UK tribunal awarded P&ID $6.6 billion, plus interest, based on what it could have earned over two decades.

The award is accruing more than $1 million in interest per day, and is now worth close to a quarter of Nigeria’s foreign reserves.