I think they'll be 3rd in votes and have 1, maybe 2 seats and the right wing will suddenly be VERY interested in Proportional Representation.I suspect they will actually win a very small handful of seats BUT be the second biggest party in terms of vote share.
I'm thinking there must be a massive "shy Reform" vote the polls haven't successfully accounted for, like the shy Tory vote before everyone turned on them, but potentially even more under-estimated because the media (rightly) portrays Reform as so explicitly racist/hard right and the Karens won't want it known