One of Singapore's top lawyers, Senior Counsel Davinder Singh, is leading a Brunei team that is prosecuting a high-profile graft case in the kingdom.

The case involves Brunei Shell Petroluem (BSP), which is said to have suffered more than $5 million Brunei dollars (S$5 million) in losses due to corruption.

Last week, the first of eight persons who allegedly received the bribes was convicted and jailed.

Aidah Tengah, 44, a former BSP staff member, pleaded guilty to the charges against her and was sentenced on Thursday last week to five years' jail and fined $200,000.

The Brunei High Court also ordered her to pay $120,000 in costs to the prosecution.

Aidah was charged with 20 counts of corruptly receiving bribes totalling $200,200 from David Chong, the manager of Musfada Enterprise, a key BSP contractor.

Musfada supplied items such as oil spill kits, box pallets and safety equipment. Chong, a Malaysian, was the mastermind who orchestrated the bribes paid between 2007 and 2009. He was sentenced to six years' jail in 2013 for his role.

Mr Singh's role in prosecuting the ongoing case, assisted by Drew & Napier lawyer Gary Low and supported by Brunei legal counsel, underscores the premium placed by the Brunei government on the case, given BSP's status as a public body.

The judge who sentenced Chong highlighted how BSP is the backbone of Brunei's economy, accounting for more than half its gross domestic product and 90 per cent of its total export earnings.

The bribes paid to Aidah were for creating purchase orders to commit BSP to purchase various products supplied by Musfada.

The total amount paid for the Musfada products amounted to about $6.4 million, but most of them were not delivered.

This resulted in losses of about $5.5 million to BSP.

Mr Singh argued for a heavy jail term, given the aggravating factors, including the huge losses BSP suffered.

Brunei High Court Justice Steven Chong agreed. He said those in positions of public trust "should expect severe sentences if they allow their personal greed to overshadow their responsibility and accountability".