1. Dear Liz, the former partner can only place a restriction on the property is she claims an interest in the property and intends contesting this issue of ownership in court. So here, the former partner will most likely issue family law proceedings or else, some form of equity proceedings whereby she will claim that, by reason of her contributions to the mortgage repayments she is entitled to an interest in the property.
2. Here, if your brother and his former partner were unmarried, then the only way the former partner can claim an interest in the property is if she made a contribution to the purchase price, or if, she made contributions to the mortgage repayment amounts. These are the two situations in which she can seek to claim an interest in the property. The position would be different if there was children of the relationship as then she might additionally, claim maintenance payments.
3. Accordingly, your brother's best approach, if a restriction has been registered, is to seek to have it removed and the issue of whether his former partner has an interest, litigated. He is best off avoid matters dragging out until he does in fact need to sell, because then he will be more susceptible to making a payment to her to "buy her off" the property.
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