I'm not all that certain that under your circs you'd stand to lose as much as people say. For sure, under the Civil Partnership and Certain Rights and Obligations of Cohabitants Act
2010 (Sn 173), your partner could go to the courts to seek property rights and redress, but the court would take all of the circumstances into account.
Have you considered a cohabitants' agreement, to govern this? I'm copying Sn 202 below. Note that you both need to have satisfied certain conditions; that it COULD provide that your partner cannot apply under Sn 173 for redress; and that the court can vary or set aside altogether the agreement (I've put these bits in bold. Hree it is:
"(1) Notwithstanding any enactment or rule of law, cohabitants may enter
into a cohabitants’ agreement to provide for financial matters during the relationship
or when the relationship ends, whether through death or otherwise.
(2) A cohabitants’ agreement is valid only if—
(a) the cohabitants—
(i) have each received independent legal advice before entering into it, or
(ii) have received legal advice together and have waived in writing the right
to independent legal advice,
(b) the agreement is in writing and signed by both cohabitants, and
(c) the general law of contract is complied with.
(3) Subject to subsection (4), a cohabitants’ agreement may provide that neither
cohabitant may apply for an order for redress referred to in section 173, or an order
for provision from the estate of his or her cohabitant under section 194.
(4) The court may vary or set aside a cohabitants’ agreement in exceptional
circumstances, where its enforceability would cause serious injustice."
(5) An agreement that meets the other criteria of this section shall be deemed to
be a cohabitants’ agreement under this section even if entered into before the
cohabitation has commenced."
HeatherJ