Pension Sharing
You can’t share a pension without a divorce and a court order. Any of the other financial transactions that a separating couple can agree on (eg maintenance, lump sum, property transfer) can be done voluntarily without involving the court. The one exception is pension sharing, for which you need a court order. Because the court is not allowed to make any sort of financial order unless there is a decree nisi of divorce, you need to be getting divorced as well.