Below is the quote from the relevant Government website. I don't believe we are at odds when there IS a clause in an employment contract. I'm merely reflecting that I've never put such a clause in a contract and have always been able to offer an employee this (i.e. avoidance of some tax/NI) as a carrot to go early. There seem to be 2 players on your side of the net now - that's not on.
Is your notice pay taxable?
If you work your notice, you'll be taxed at the usual rate on the money you earn in your notice period. PILON is only taxable if it's been provided for in your contract or is customary. Otherwise, it is not taxable unless the PILON together with redundancy and other compensation adds up to more than �30,000, in which case the excess over �30,000 is taxable at the usual rate.