The organisation, which represents chief executives, said it found that high salaries were "unusual".

According to the IoD's figures, directors of companies with a turnover of up to £35m earned on average just £55,000 in salary last year and received an annual bonus of only £12,500.

As companies get larger, so do salaries. In businesses with a turnover of £25m to £200m, managing directors received avarage salaries of £87,500 and a bonus of £17,000.

Top earners are bosses of firms with a turnover of more than £200m. They can expect around £140,000 a year, plus an average bonus of £33,650.

According to government statistics, 99% of companies in the UK have a turnover of less than £10m.

The IoD's Director General, Tim Melville-Ross, said the survey showed that average pay increases continued to be modest. Pay rises were in the range 3.5 to 4.5%, and spectacular salary increases were the exception.

Mr Melville-Ross said: "This year's survey also shows that, reflecting the economic climate we are now in, directors are expecting smaller increases in the next 12 months."

However, even though salaries may not be rising, bonuses are. In 1992 to 1993 the bonus accounted for 12.8% of the total remuneration package of company directors, today it weighs in at 18.5%.

During recent years there has been repeated outrage over large pay rises. Directors of privatised utilities, for example, saw their pay rise by 18% on average.

Government ministers were irked by reports of similar rises in other sectors, which did not help their calls for general pay restraint.