In a letter to Britain's home and foreign affairs ministers, a coalition of close to 50 NGOs said the long-delayed confiscation process had undermined the strong anti-corruption message sent by Ibori's conviction over a decade ago.
"The years of disruption and delay in recovering and returning these stolen assets means this message has so far rung hollow for the Nigerian people," said the letter, made public on Thursday by one of its signatories, Spotlight on Corruption.
A former governor of oil-producing Delta State in southern Nigeria, Ibori pleaded guilty in a London court in 2012 to 10 counts of fraud and money-laundering and was handed a 13-year jail sentence, of which he served about half before going home.
Still influential in Nigeria, Ibori has had meetings with President Bola Tinubu in recent months and has friends and associates in other powerful positions.
The NGOs, which also included Transparency International and Africa Network for Environment and Economic Justice, said funds confiscated from him should go to projects benefitting the people of Delta State and implementation should be subject to civil society monitoring.
Efforts by British prosecutors to confiscate Ibori's assets began in 2013 but have run into repeated obstacles and delays in the London courts.
In July, a judge ordered the confiscation of 101.5 million pounds ($123.9 million) from him, one of the biggest orders under Britain's Proceeds of Crime Act 2002 since it came into force.
He has applied for leave to appeal against the order and his application is at the early stages of the appeal process.
By Estelle Shirbon, Reuters