Answer
No, a postnuptial (postnup) and a prenuptial agreement (prenup) are different.
A prenuptial agreement is a contract that is entered into by a couple before they marry or enter into a civil partnership. It outlines how the couple wishes to divide their assets and finances in the event of a divorce or dissolution. While it is not legally binding in the UK, it clearly demonstrates the intentions of each party.
On the other hand, a postnuptial agreement is similar to a prenuptial agreement but is entered into after the marriage or civil partnership has taken place. It serves the same purpose of outlining the division of assets and finances in case of a future separation or divorce.
The main difference between the two is the timing of when they are created before or after the marriage/civil partnership.