An unelectable extremist who hijacked their party has already served as prime minister – her name was Margaret Thatcher

There’s a leadership battle. The party is torn between left and right. A candidate considered unelectable unexpectedly wins, creating an ideological rift. The knives come out, with fears the party will never win an election again. But the new leader sticks to their guns. They doggedly push through, and cause the biggest ideological shift in the party’s history.