I believe that the issue lies with the fact that the company provided you with the insurance as a benefit and that the payout is coming from the insurance company, and not your employer directly.
Therefore the payment you receive will not be a "termination payment" but rather will be the the settlement of an insurance claim that was triggered by your termination.
ie, if your employer were to pay you the lump sum themselves it would probably have been tax free but they aren't. They simply paid the insurance premiums over the course of your employment & the policy is now paying you for your claim resulting from the loss of your licence.
I know of a pilot that a similar thing happened to and he was taxed on his payout because he was the insured party (and therefore received the benefit directly), not the company.