For instance, if you chose to sacrifice £100 per month the total amount paid into your pension scheme per month is £106.90. (£100.00 x 13.8% / 2 = £106.90)"
This might be obvious but you're sacrificing pre tax income. So if you pay 40% marginal tax, you are sacrificing (£60 minus whatever the employees NI is) to get the £106.90.
You mean "be careful telling them to sacrifice a large amount coz you might not have any money for beer afterwards" if I forget they're still taking tax off the reduced amount later?
This might be obvious but you're sacrificing pre tax income. So if you pay 40% marginal tax, you are sacrificing (£60 minus whatever the employees NI is) to get the £106.90.