You can have a separation agreement to sort out the finances but it won't be legally binding until after there is a Decree Nisi in place. AFAIK It also cannot include a pension sharing order as this has to be made by the court. You could have this agreed in principle though.
If the separation agreement is properly drawn up and agreed after full financial disclosure, it can carry weight in the future and could form the basis of a Consent Order when you do file for divorce at some point in the future. Do bear in mind that, if circumstances change, the agreement can be revisited.
This site offers a Separation Agreement service (others are available) that you may want to have a look at. Click on the services tab.