Over four million people have now been auto-enrolled into a workplace pension scheme, according to latest figures from The Pensions Regulator.
TRP's monthly figures, published today, show that 4.032 million people are now paying into a workplace pension.
Pensions minister Steve Webb said the 4 million figure was a 'milestone' and showed that saving into a workplace pension was 'now becoming the norm'.
'Four million people have now been automatically enrolled into a workplace pension with many more saving for their retirement for the first time or saving more as a result,' he said.
'This policy is helping to build a fairer society as millions of workers who didn't have the chance to save in a workplace pension before are now on track for a more comfortable retirement.
'And while people have the choice to opt out of workplace pension saving the overwhelming majority are staying in, ensuring a better future for themselves and helping reverse the savings slump in Britain.'
Introduced in October 2012, auto-enrolment will now be extended to smaller employers, which need to begin to enrolling their workers into pensions. All UK employers are due to be using auto enrolment by 2018.
Charles Counsell, TPR's executive director of auto-enrolment, said: 'A seaside hotel, a scrap yard, hi-tech factories, colleges, care providers, hairdressers and a designer all feature among the wide range of employers completing their duties this month.
'It is a mix which illustrates just how automatic enrolment is gradually becoming part of the fabric of running every type of workplace.'
Responding to the figures today, Joanne Segars, chief executive of the National Association of Pension Funds, said it was 'excellent news for UK savers'.
'Pension schemes and employers have put huge amounts of work into setting up and enrolling workers into millions of pension accounts.
'Workplace pension schemes have always provided one of the very best ways to save for retirement, and automatic enrolment offers the greatest chance of getting people into the habit of saving.'
But Tom McPhail, head of pensions research at Hargreaves Lansdown, said nearly 4.5 million employees were still missing out on workplace pension membership, while a further 4.5 million self-employed workers were not covered by the scheme.
'Only last week the DWP produced updated analysis which shows that 11.9 million people are under-saving for retirement,' he said.
'Very broadly, anyone who is not contributing at least 12% of their salary a year to a pension probably isn't saving enough. In the meantime, auto-enrolment has been cited as one of the downward pressures on earnings growth.'