Salary Sacrifice Changes from April 2017 Sacrifice allows some employers and employees to pay less Income Tax and NICs by replacing cash salary with Benefits In Kind (BiKs) – such as private healthcare, mobile phone, a company car, a gym membership
The measure will limit the Income Tax and employer National Insurance contributions (NICs) advantages where BiKs are offered through salary sacrifice or where the employee can choose between cash allowances and BiKs.  Salary sacrifice is a contractual arrangement between an employee and their employer involving a reduction of an employee’s cash pay in return for a BiK, such as a phone or a car.  For some BiKs the value used for calculating tax and NICs liability is less than the amount of the cash pay forgone, allowing the employee and employer to choose to pay less tax and NICs than they would otherwise. The measure will fix the taxable value of those BiKs provided through salary sacrifice at the higher of the amount of cash forgone or the amount calculated under the existing BiK rules.
There will be no change to the tax and NICs advantages of salary sacrifice arrangements for:pension saving into a registered pension scheme, employer provided pensions advice, employer-supported childcare, cycle to work schemes or Ultra Low Emission Cars (ULEVs).  Further, those already in contracts for BiKs involving salary sacrifice will be protected for the length of that contract, subject to final backstop dates.

You can find more detailed information here