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If you both want a "clean break", then you will need to instruct a Solicitor to prepare a separation agreement or Consent Order. Both will confirm the details of the division of assets and would then normally prevent the other from claiming anything further in the future (in the case of a Consent Order, this is legally binding on both parties full stop, whereas the terms of a separation agreement can sometimes be challenged by one party at a future date if the circumstances of the parties change).
A Consent Order can, however, only be signed if you are going through a divorce, so ideally one of you will need to issue a divorce petition and once the Consent Order has been signed, you are safe in the knowledge that no further financial claims can be made.
I hope this assists and sets out the legal position.