Total membership of occupational pension schemes in the UK was an estimated 41.1 million in 2017, the data showed, compared with 39.2 million in 2016 and is the highest level recorded by the survey.
Total membership of public sector pension schemes was 15.5 million in 2017, compared with 14.8 million in 2016.
In occupational pension scehemes, the number was 15.1 million in 2017, split between the private and public sectors.
Defined contribution schemes also saw an increase, with 7.7m in 2017 compared to 2016's 6.4m - but the contribution rate fell in 2017, with the average total - consisting on member and employer - contribution rate falling to 3.4% from 4.2% the previous yea.
Nathan Long, senior analyst at Hargreaves Lansdown
"The growth in pension savers shows auto-enrolment has been spectacular at changing the financial future of the nation. Attention should now shift to helping everyone gain the confidence to take control of their own retirement if they want to.
"The amount people are paying in needs to rise, but will automatically go up to 8% of earnings when rules change in April next year. Hargreaves Lansdown have found half of people can already be helped to voluntarily increase their contributions, so the challenge is to improve on this as savings continue to grow.
"The number of dormant pension pots is increasing with all the speed of a runaway train. Giving people the opportunity to pay into their choice of pension when they join a new employer would help put the brakes on before the problem threatens to de-rail the auto-enrolment project."
