An ex-Goldman Sachs banker has been sentenced for four and a half years for laundering money on behalf of one of Nigeria's most infamous politicians during the height of his power.

Elias Preko, helped James Ibori, the ex-governor of the oil rich state of Delta to launder his money and was convicted at London's Southwark Crown Court.

Preko became the fifth person to be convicted and sentenced in an elaborate case involving a number of people involved in corrupt activities during Ibori's reign as governor of Delta.

Ibori is currently serving 13 years in a British jail after pleading guilty to at least 10 counts of fraud and money laundering in 2012.

Ibrori's demise has been closely watched in Nigeria where his rise to power and fall from grace could be seen as a tale of the political corruption which has blighted the oil rich country for many years.

Preko who is 54 and a Harvard graduate, is the latest of Ibori's associates to be jailed for assisting his corruption after the ex-governor's wife, mistress, sister and lawyer were all convicted by British courts in previous trials.

A jury unanimously convicted Preko of two offences of money-laundering between March 2003 and April 2008 when he was arrested.

He was charged with assisting Ibori in channelling stolen money through a web of offshore trusts and shell companies.

"The evidence against you in this case was very clear. You knew what Mr. Ibori was doing and you were actively assisting him," said Judge Anthony Pitts to Preko in his sentencing remarks.

"You are a man of considerable ability and intelligence, highly educated, capable of making lots of money perfectly legitimately," he continued.

The court had heard that in a decade at Goldman Sachs, where Preko was in charge of private clients in sub-Saharan Africa, Preko earned $12m (£7.3m, €8.7m).

Preko had left Goldman Sachs before he committed the offences and the bank is not accused of any wrongdoing.

"You had the ability to walk away (from Ibori). You chose to involve yourself with him as a professional man, against the code of upstanding conduct for men in your position," Pitts added.

The judge noted that the sums Preko had helped launder were "relatively small amounts in a case where the amounts are almost beyond belief".

Ibori was in his heyday a power broker at the heart of Nigeria's ruling party when he was the Delta governor from 1999 to 2007

After he left office and lost immunity from prosecution his fortunes changed for the worse with political developments in Abuja until he was extradited from Dubai to Britain in 2011.