Figures from the The Pensions Regulator show that up to the end of May 2014, 15,099 employers had hit their staging date and enrolled 3,633m employees in an auto-enrolment scheme.

However, a Freedom of Information Request from Hargreaves Lansdown found that from 1 October 2012 up to 1 May 2014, 22,940 employers should have hit their staging date.

Thousands of workers at the country’s largest firms have already been enrolled into a workplace pension under the scheme. Small and medium sized employers will join between now and 2018.

Tom McPhail, head of pensions research at Hargreaves Lansdown, said: “It isn’t yet clear whether this shortfall in scheme reporting is the result of delays in the registering of schemes which are fully compliant, or in fact it is attributable to thousands of employers failing to hit the deadline. We’ll find out one way or the other over the next couple of months.”

Under auto-enrolment rules, any worker aged between 22 and state pension age earning more than £10,000 a year must be enrolled into a workplace pension scheme.

McPhail said: “More employees have been missed by auto-enrolment than have been put into a pension.  This doesn’t mean auto-enrolment was a bad idea but it does show that more policy solutions are needed.

“Millions of employees are missing out on a pension contribution from their employer and have nothing but the state pension to look forward to. We’d like to see greater emphasis put on employee engagement, both for pension scheme members and for the ineligible employees who need to be encouraged to make provision for their retirement.”