Please see the “alternatives to divorce” section but, in short, a separation agreement can be entered into by parties who have separated but who, for one reason or another, do not wish to divorce (at least in the short term). Such an agreement should be prepared, ideally, by a solicitor so that it covers all of the points that need to be made but parties who enter into a separation agreement need to be aware that, upon a subsequent divorce, the separation agreement will be one (albeit likely to be a significant one) of a number of factors that a court would be required to take into account in the absence of any agreement between the parties in determining the issue of finances.
Please also see the explanation of the judicial separation process in the “alternatives to divorce” section.