"Can employers claim the contributions they pay into pensions back as a tax-deductible expense? "
Yes - contributions to a registered pension scheme by an employer are allowable as a deduction in their trade profits for tax purposes.
However, tax relief isn’t automatic and it’s up to the employer’s local inspector of taxes whether or not the employer receives tax relief on the whole contribution.
Contributions must satisfy what is known as the ‘wholly and exclusively’ requirements to receive tax relief. So it’s not always possible to find out up-front whether an employer contribution could be claimed back as a tax deductible expense.
This is a complex subject and more details can be found on the government’s website.