It sounds like the OP doesn't understand her legal rights and probably doesn't have enough cash to pay a lawyer.
She talks about "being on the mortgage", but doesn't mention the deeds, she hasn't confirmed whether they own as joint tenants or tenants in common, and she seems to have accepted the idea that her ex should get to keep the house and that her entitlement to it is limited to her financial contributions anyway.
In that context, can she really be blamed for not managing to force a sale of the house? It doesn't sound like she has the first clue how to go about that.
The situation has now come to a head because the government is saying that she must repay an amount of Universal Credit that exceeds the amount her ex partner says she is entitled to from the house. Clearly this would be an incredibly unfair outcome and she needs to find a way to fight it.
And as difficult as it will most likely be to force a sale of the house, she's more likely to be able to force her ex to sell a house she owns part of than she is to convince the government to waive a large debt.
The first step is to find out how the house is owned (joint tenants, tenants in common in equal shares, or tenants in common in unequal shares), roughly how much the house is worth, and how much equity is in it.
This means she needs:
- the legal documents from when they bought the house and ideally copies of any legal advice they were given by their conveyancing solicitor at the time;
- at least one current valuation by an estate agent; and
- confirmation of how much is left on the mortgage.
As an owner of the property she is entitled to get all of this information and ex is not entitled to withhold it from her.
Once she has that information she can write back regarding the UC claim and say:
- I have looked into how the property is owned and estimate that I am entitled to X amount of equity in it (better to err on the side of lowballing this estimate).
- I have not lived in the property since X date because my ex partner refuses to leave, and I also cannot afford to rent privately which is why I am living with my parents.
- My understanding based on the advice you gave me on X date is that my equity in the house would not affect my entitlement to claim UC. I now understand this advice was incorrect but I have no practical means of repaying the last three years of UC payments, which I used for the purpose for which they were intended (to live on).
- I am going to put the wheels in motion to force a sale of the house but I understand that this could take time, given that the co-owner is completely uncooperative. Until the house is sold and I can get my equity out, I have no means to repay this debt.
- Please advise on the options available to me.
Another thing she could do, which is admittedly an extreme option and does not apply if her ex is in any way abusive, is to simply move back into the house and piss him off so much that he agrees to sell it within a fortnight. Say, "The government are forcing me to repay three years of UC because they say I own this house, and that means I have no choice but to move back into it."
If, on the other hand, her ex is abusive, she should add the following point to her letter:
- I cannot move back into the house and it is difficult for me to even get near it for the purposes of valuations and estate agent viewings, because I was a victim of domestic abuse by my former partner who still lives in the house.
I understand that allowing people who own properties they do not live in to claim universal credit is a loophole that unscrupulous people would exploit. But at the same time, I think that taking into account someone's joint ownership of a house they cannot live in and cannot get their money out of is also a loophole in the system that leaves people like the OP (mostly women, I reckon) extremely vulnerable.