Of course it's a bloody tax!
Now, on the bright side - depending on who you work for.
In my company they tell you in your contract that your indemnity is calculated on your basic salary only, and excludes any allowances you might get.
GOSI, on the other hand, who decree what the 1% is based on, actually do include these allowances.
Which means a fair chance that when you come to pick up your EOS, you can reasonably argue that it should be based on what GOSI call your earnings.
Also remember you have one year after you leave to file a case in labour court for what you might be owed. Time to start finding labour lawyers willing to do a no-win no-fee deal for you (and I believe there's a few that will when they see how obvious this one is <heh>).
Of course if you haven't been around long ignore this message