The answer lies in your own post from that earlier thread, i think. You said in that thread, quoting from an HMRC letter:
"your contributions are refunded with interest, and the payment of a single, non-returnable premium covering the cost to the pension scheme of providing post-retirement survivor's pension, in the event of your marrying (I am not married) or entering into a civil partnership and dying before your spouse of civil partner. The premium is 30% of the value of the contingent post-retirement survivor's pension.
Under the tax legislation introduced by the Government with effect from 6 April 2006, lump sums such as this, which are not paid as part of a pension, are generally considered 'unauthorised' and would be liable to a tax charge. Because this is "unauthorised' payment under the new tax legislation you will be liable to pay tax at 40% of the amount paid to you. We will pay you your refund without tax deducted but it is then your responsibility to tell Revenue that you have received an unauthorised payment from the scheme. Please note we will tell Revenue that we have made this payment to you and they will follow this up with you in due course.