The case referred to is LB v Rosett and is well known but contains only the blindingly obvious. Didwot misunderstands the use of the word "detriment". Herewith the case summary:-
(a) The finding of an agreement or arrangement to share the property can only be based on evidence of express discussions between the parties, however imperfectly remembered and however imprecise their terms. Once a finding to this effect is made it is then only necessary for the claimant to show that in reliance on this agreement she acted to her own detriment or significantly altered her position.
(b) Where there is no such evidence, then the court must rely entirely on the conduct of the parties as the basis from which to infer an intention to share the property. Direct contributions to the purchase price by the claimant, whether initially or by payment of mortgage instalments, will justify the necessary inference. It is extremely doubtful whether anything less will do.
In practical effect, if your matter gets to Court each of you will spend three to five days giving evidence and being cross-examined, and each of you stands the self same equal chance of winning at the beginning. But it is a gamble, and nobody can predict the outcome with certainty. One very important thing to remember is that the Judge will read all of the paperwork and will have formed an initial opinion before he appears, so go over the paperwork with a fine toothcomb with your legals to ensure that your defence is fully documented and easily understood.