Soldato
It's pretty simple. There is a very short list of items which are NI and tax free under salary sacrifice.
Childcare vouchers
Additional employer pension contributions
Cycle to work schemes
Company cars
Work-related training
Car parking near your workplace
There is then a longer list which incur NI but are tax free.
Everything else like PS4 will be taxed and NI just like you had got paid the full amount of money on your wages and your employer will declare this on your P11D.
In general, salary sacrifice schemes are only beneficial for the employee for items which are at least tax exempt.
Everything else is just paying in instalments and sometimes if you are tied down to a supplier, it might not have been the cheapest place to purchase it from anyway.
That makes more sense - apparently a gift voucher is considered readily convertible when I assumed not. As I said, not an expert!