The Nigerian police force has rejected the conclusions of a new report that it is regarded as one of the country's most corrupt institutions.
Ex-police chief Tafa Balogun was arrested last year
A police spokesman said the force had the highest quality control system.
He said the Centre for Law Enforcement Education (Cleen) survey did not reflect changes implemented since the arrival of the new inspector general.
Last year, Nigeria's former police chief was found guilty of corruption and sentenced to six months in prison.
The other institution named in the survey as corrupt is the country's national electricity provider, the Power Holding Company of Nigeria (PHCN).
PHCN officials are alleged to have demanded money for maintaining power supplies.
Nigeria is routinely ranked as being seen as one of the world's most corrupt countries by watchdog Transparency International.
According to Cleen director Innocent Chukwuma, their survey was conducted across Nigeria between October and December last year.
He said that those surveyed were asked about their "perception of corruption - whether it had decreased or increased in the last seven years of President Obasanjo's government when a lot has been put into the fight against corruption".
This included a question on how they regarded government agencies.
"Seventy-eight percent of the respondents say that corruption has indeed increased," he told the BBC's Focus on Africa programme.
But police spokesman Haz Iwendi said surveys were easily manipulated.
"This survey does not reflect the present reality on the ground, there are lots of changes going on," he told the BBC.
He said the police were actively exposing those who were corrupt within the service, unlike other government agencies.
"Nigeria's police has the best quality mechanism in this country - there's no organisation that cleanses itself like the Nigerian police force."
Meanwhile, the most senior Anglican cleric in Nigeria, Archbishop Peter Akinola, called on the government to do more to uproot corruption.
Archbishop Akinola complained that few people accused of corruption were being put behind bars.
Speaking ahead of a national conference of the Church of Nigeria, he called on Nigerians to vote against any corrupt politician standing in the general elections scheduled for next year.