Benn, Umana, etc don't have much of a career ahead of them as members of an unelectable party - better to take a deep breath, form a grand alliance with the pro-EU centrist wing of the Conservative Party (who also won't have much of a career ahead of them when the Fat Philanderer takes over), force a general election and fight it on a Stop the Negotiations ticket. Wait a few months for the economic disasters of 23 June to start biting and, who knows.
Yeah, that's possibly an option. One of the things this referendum has thrown up is a new division in British (or at least English and Welsh politics). The Establishment vote (Remain) came largely from the metropolitain areas. The "F**k you" vote came from an alliance of the Tory Shires and the old Labour heartlands, two areas that believe they've been abandoned and shat on by all the traditional metro-centric parties. Maybe we need new parties to reflect these new divisions.