Buster - your ex's solicitor is under no duty to give you advice, and it would be improper of him to do so in view of the obvious conflict of interest. Get advice on your own account.
Your original query was whether it is possible to
have a beneficial interest in a property if one is not the legal owner.
I said that in principle, yes, it could - but in my view, there would have to be a contribution of a financial nature such as helping with the deposit or paying for repairs or an extension. The burden of proof is on whoever is making the claim.
The problem that I find here is something like this.
The first is that only the legal owner of property ( or joint owners ) can legally mortgage the property.
Secondly, a mortgage deed will contain covenants by all the borrowers to repay the sum borrowed plus interest. It seems unlikely that your ex is going to agree to repay the mortgage loan on a house in which she has no interest.
I'm afraid I have to be straight with you and say that nobody on wiki could offer you more than very general advice. You use the expression ' girlfriend ' from which I deduce that she is not, and never has been, your wife.
And neither can I advise on documents which I have not seen.
On the information you give, I believe your solicitor has acted properly. It's quite an esoteric field of law and I would not be confident that I could give you accurate advice when I have been out of practice for so long.