David Owen

New party, and a refusal to merge. A former Labour Foreign Secretary, Owen co-founded the SDP and led it from 1983, then refused to join the 1988 merger with the Liberals and kept a rump 'continuing SDP' going until it was outpolled by the Monster Raving Loony Party at the 1990 Bootle by-election and wound up. He later sat as a crossbencher in the Lords and backed Brexit. His career shows the costs of crossing a line twice.