It makes sense, but the Court would still entertain a claim from her. Indeed, the Court would not look kindly at him effectively trying to defeat her claim in that way. If I am right, it sounds as if he owned the property before she moved in. Depending on what they may have said to each other and what monies have been expended she may be able to persuade a Court that she has a beneficial interest under Trusts of Land and Appointment of Trustees Act (Tolata). However, the biggest danger for him is an application under the Children Act since they have a child together.
Plus of course, if the gf is half sensible, she'll have put a restriction on the title which will prevent a conveyance in any event.