Hi MrsH,
Any deduction from pay, outside of a very specific list of exceptions, is likely to reduce a workers minimum wage pay.
Salary sacrifice will always reduce a worker's minimum wage pay.
The worker is in essence giving up that portion of their pay in exchange for something else, so it cannot be included in any minimum wage calculations.
Any determination would depend on the arrangements in place.
For more information, please refer to:
Calculating the minimum wage Salary sacrifice
Thank you.