Figures released by the Department for Work and Pensions confirmed that three-quarters (76%) of workers excluded from auto-enrolment when the threshold is lifted from £8,105 to £9,440 in 2013-14 would be women.

In all 320,000 women out of a total of 420,000 individuals would be left out from the process when it is introduced.

Replying to a written question from shadow pensions minster Gregg McClymont, Webb said: “We estimate that there are 11 million workers eligible for automatic enrolment into a workplace pension of whom 37% are women.

“Raising the value of the earnings threshold at which individuals become eligible for automatic enrolment, from £8,105 to £9,440 would exclude around 420,000 individuals, of whom 320,000 are women.”

However, the Liberal Democrat minister also noted that these people were still eligible for entry into a workplace pension.

“Anyone who is not automatically enrolled because of an increase in the earnings threshold will retain the right to opt in,” he said.

“If they earn above the lower limit of the qualifying earnings band, which currently stands at £5,564, they will also get an employer contribution. Employers are required to provide information about these opt in rights to individuals,” he added.