The starting point for the sharing of assets in a marriage is 50/50 of all assets accrued during the marriage. The court would typically look at the needs of each party, the needs of any minor children of the marriage, and the factors as listed in s25 of the Matrimonial Causes Act 1973, which I will link to below.
It is important to note that the finances will only be reviewed by the court after the decree nisi (now called ‘conditional order’) has been granted, and will only take effect after the decree absolute (now called ‘final order’).
You will need to attend mediation (see link below on where to find a mediator) before you can make the application to court in any case, and can therefore agree everything ahead of the time to make the application to court. If you can agree, you can get a consent order drawn up, and the court will then seal that as a consent order (i.e. an agreement between you). Sealing the order makes it enforceable. If you cannot get agreement for a consent order, one of you will need to apply to court on Form A, and the court will list the matter for a hearing to see if a Judge can help you agree. If you still cannot agree, the matter will be set down for a new Judge to decide how to split the assets.
You will both also need to complete full financial disclosure, so each of you, and ultimately the judge, can see what assets there are and what is available to share. This includes everything from savings, property to pensions etc.
Until you each have full disclosure it is impossible to say what the potential outcome will be, but as stated above, the starting point for a long marriage is 50/50. There is no magic formula to use, just the law as described and the judge’s absolute discretion on the final decision based on that law.
Find a mediator: www.familymediationcouncil.org.uk
Section 25: https://www.legislation.gov.uk/ukpga/1973/18/section/25/1997-06-19?timeline=true
Form A: https://www.gov.uk/government/publications/form-a-notice-of-intention-to-proceed-with-an-application-for-a-financial-order
Form E: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/953463/form-e-eng.pdf
Find a solicitor: solicitors.lawsociety.org.uk