Some Iraqi police officers in Basra are working for Shia Muslim militias and carrying out sectarian violence, the UK's chief police adviser has warned.
Mr Colbourne said some Iraqi officers were corrupt
Mike Colbourne, assistant chief constable of Bedfordshire, admitted there were officers who were guilty of corruption, kidnap and murder.
But he said the situation was getting better and promised UK forces would not leave until Iraqis were ready.
He told BBC's The World at One "We know that there are bad apples."
Mr Colbourne said that in spite of an anti-militia drive by the new provincial director of police, Major General Jaleel Khalaf Shuwail, a number of officers were still linked to violence.
He added: "The corruption that we are talking about does range from financial corruption through to serious offences such as murder, kidnap.
"There are a number of Iraqi police service officers who are clearly aligned to militias.
"I think it is fair to say that there is sectarian violence that is being committed by both police officers and other Iraqi security forces officers.
"That is just the truth of the situation as it is at the moment.
"We know that there are bad apples and there are a significant number of both serving, but also those who have been sacked and retired, officers who continue to agitate and continue to be involved in violence."
Mr Colbourne said that British police advisers were helping Iraqi officers to drive out corruption from their ranks.
BBC Middle East editor Jeremy Bowen said it would have been easier to address the problems as they were building up after British troops captured Basra in 2003 and not now, when the end of the British occupation was in sight.
He added that Mr Colbourne's comments came at a time when Britain was being widely criticised for losing control of Basra.
'Hearts and minds'
The respected International Crisis Group, in a report earlier this summer, said that Basra was controlled by rival Shia militias, and British forces there appeared to have given up trying to impose the rule of law.
But Mr Colbourne insisted that British forces would not pull out until their Iraqi counterparts were ready to take over.
"We are not looking to leave Iraq. We want to leave Iraq when the job is done, when we actually have got an effective Iraqi security force structure that is going to support a peaceful transition," he said.
"It is the hearts and minds and intentions of those officers and how they then relate to the wider public which now is concerning us.
"They know that there will be an end date. They know that we will be leaving Iraq and when we do leave Iraq they do need to be able to step up their game to take on the role of policing and they have got to do it well."