Hi Alexander Darling,
Since 6th April 2017 changes to the legislation mean that the tax and National Insurance Contributions (NICs) advantages where benefits in kind (BIK) are provided through salary sacrifice (called Optional Remuneration Arrangements (OpRA) in the legislation) are now largely withdrawn and taxable.
Exemptions to this are childcare,cycle to work, pension advise, pension contributions.
For further understanding please see:
EIM42750 - Salary sacrifice: what is a salary sacrifice: arrangement of guidance
Thank you.