It found 15 per cent of firms would also demand compensation for the time staff spent training away from the workplace.
Nearly a fifth said there was nothing that would persuade them to invest more in training, says the report, titled Employers' Perspectives on Improving Skills for Employment.
The Association of Colleges said the findings expose a flaw in Government policy to persuade employers and individuals to pay more for training.
Julian Gravatt, the AoCs director of funding and development, said: "It is proving difficult to procure more fee income from employers. Individuals are more willing to pay higher fees than businesses."
He said the Government needs to explain to employers the benefits that training will bring to their businesses.
The NAO, which scrutinises public spending, also said more employers in England needed to be persuaded of the value of training. It advised the Government to simplify information about basic courses it offers, work closer with employers to find out their training requirements, and tailor funding to encourage employers to meet skills shortages and "regional priorities". It said investing in training would bring increased profits and wages.
The report revealed that 6 per cent of employers have skill shortage vacancies and 20 per cent have skills gaps, costing pound;10 billion a year in lost revenue.
Auditor general Sir John Bourn said: "The doubts that some employers have about the value of skills training must be addressed by more streamlined communication with employers, by developing flexible and affordable training targeted on business needs, through incentives to employers, and effective channels through which employers can influence skills training."
A spokesman for the Department for Education and Skills said: "Evidence shows that higher skills levels help productivity and bottom line.
Employers need to recognise this and play their role by investing in training."