Edgar v Edgar [1980] EWCA Civ 2
Sets out the extent to which a contractual agreement for a clean break provision is to be reflected in the subsequent exercise of judicial discretion.
http://www.bailii.org/ew/cases/EWCA/Civ/1980/2.htmlXydhias v Xydhias [1998] EWCA Civ 1966
When parties agree to settle on terms a court may have to consider whether the terms were invalidated by a factor such as non-disclosure
http://www.bailii.org/ew/cases/EWCA/Civ/1998/1966.htmlG v G (Financial Provision: Separation Agreement) [2004] 1 FLR 1011
It was said a separation agreement could be given considerable weight, notwithstanding it having been made at a time when judgment was likely to be clouded. Sorry I don't have url to hand.
Soulsbury v Soulsbury [2007] EWCA Civ 969
Comments on the status of agreements between the parties, suggesting that, provided they did not prevent one party from applying to the court for relief, such agreements could be enforceable, even if not converted into a court order. Lots of references to other judgements.
http://www.bailii.org/cgi-bin/markup.cgi?doc=/ew/cases/EWCA/Civ/2007/969.html&query=title+(+soulsbury+)&method=booleanCoud be more specific If you give more details.