A salary sacrifice will lower your National Insurance Contributions whilst boosting your pension, but the amount you could borrow for a mortgage and your entitlement to statutory benefits will both decrease.
An umbrella employer may offer you the option of contributing to an independently administered pension scheme under a salary sacrifice arrangement. If so, you can give up part of your salary (your sacrifice), which your employer then pays into your pension for you.
As you’re effectively earning a lower salary, both you and your umbrella employer pay lower NICs. Better still, your employer may pay part or all of their NIC saving to your pension too (although they don’t have to do this).
However, you can’t use salary sacrifice if it would reduce your earnings below the minimum wage, and there are some other disadvantages, too. For instance, a lower salary may affect the amount of money you are able to borrow for a mortgage, as well as reducing your entitlement to benefits such as SMP because your gross pay is lower.