Directors of the country's top companies have built up pension pots worth an average £4.3 million each.
The pension arrangements of 351 directors showed that the average value increased by £400,000 over the past year, according to TUC analysis.
Annual pensions are now worth more than £240,000, and are 24 times bigger than the average occupational pension, said the report.
An increasing number of top directors now receive cash payments instead of taking part in company pension schemes, with average payments of £164,000 this year, up by £26,000 on the previous 12 months.
The most common retirement age for senior executives is 60, compared with 65 for other members of pension schemes, the research showed.
The TUC said the "ever increasing" value of directors' pensions was in sharp contrast to the fortunes of the pensions of most workers, with the number of employees saving in employer-backed schemes falling.
The scale of executive "excess" had largely escaped the attention of shareholders because of the "confusing and sometimes misleading" reporting of their pensions, the TUC claimed.
General secretary Brendan Barber said: "Companies continue to chip away at the pensions of ordinary workers while awarding their directors solid platinum pensions worth hundreds of thousands of pounds a year.
"Top executives already enjoy huge pay packages that go up every year irrespective of the success of their company or the state of the economy. These salaries alone guarantee lucrative pensions so the generous packages uncovered are an insult to the vast majority of workers who are denied such favourable terms.
"The gap between the pensions of top directors and everyone else does not just reflect the excess of the super-rich, but shows just how poor pensions are for ordinary workers in the private sector, where more than two out of three get no employer pension help."
Pensions will be debated at the TUC's annual congress in Brighton next week, when delegates are expected to attack the Government and private companies over reforms, changes and cuts.
Darren Philp, director of policy of the National Association of Pension Funds, said: "It follows that people who earn more will accrue bigger pensions. But investors may have important questions about fairness if the pensions of directors are disproportionately more generous than those of other staff.
"More transparency is needed around boardroom pensions. Boards need to be open about their pension arrangements so that shareholders such as pension funds can hold top management to account."