NHS chief executive Nigel Crisp has admitted to MPs that doctors have distorted clinical priorities because of pressure to tackle waiting-list targets - but he denied that the practice was widespread.
Mr Crisp appeared before the Commons public accounts committee on Monday to discuss the findings of the National Audit Office report Inpatient and Outpatient Waiting in the NHS.
Published in July, the report caused a storm of protest, with accusations from consultants that the treatment of people with life-threatening diseases was being delayed in order to meet the government's waitinglist targets.
'No doubt that there are specific incidents where that has happened, and I have no doubt that people can see an incentive in doing that, 'Mr Crisp said.
'It doesn't mean it is widespread.Where we do come across that as an issue, we need to do something about it.
'I am not complacent.' He told the committee the practice 'is not on a level that will distort the overall [waitinglist] figures'.
Mr Crisp said the survey of consultants on which the NAO findings were based was small - 558 consultants were questioned - and unrepresentative, concentrating on just three specialties.
And he reminded MPs that consultants had to 'fit in' minor procedures in order that patients were treated and not simply left on the waiting lists.
The wide variation in waitinglist figures across the NHS which was highlighted by the report was also raised by the committee.
Stressing that the situation was 'unacceptable', Mr Crisp said it was due to a 'mix of capacity and historical capacity and in some cases how effectively the management system works'.
He said that staff numbers were the biggest obstacle to increasing capacity, but told MPs that the NHS Modernisation Agency was already spreading good management practice and more resources were being made available.
Asked why the improvements were not evident, he replied: 'These things take time.'
Following recent comments made by health secretary Alan Milburn, Mr Crisp also pledged to give patients more control over their care.
He told the committee: 'We are looking at how to introduce choice without having to go through the [internal market] again.'