That's not strictly true - the judge will base it on time together and income both brought during that time. I.e. if it is a long term relationship and the wife has given up work to look after kids then it will be 50/50. If it is a one year marriage and one earns £70k while the other earns £30k, it is more likely to be less even. Declaration of trusts usually include a clause which means they need to be reviewed upon marriage / birth of children.