The revised auto-enrolment implementation schedule will net the government £380m in reduced tax relief on pension contributions, according to budget documents.
The figures reveal changes to the staging dates - which exclude employers with fewer than 50 employees from the legislation until next parliament - will save the government £5m by 2015, £40m by 2016 and 380m by 2017.
The costing is calculated by comparing the tax relief due under the implementation schedule described in the existing legislation with the tax relief due under the revised implementation schedule.
HM Treasury said these estimates were based on extensive research but added there was uncertainty over the number of people who would be making additional contributions under the workplace pension reforms.
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