The most important issues in British political history have ended up being settled across parties. Here is a quick thread of 5 of the most consequential. But I may be forgetting others of similar importance.
The two neck-and-neck 1910 elections wipe out Liberal landslide of 1906, so government needs Labour and Irish votes in the Commons and (finally) grudging Tory 'hedger' votes in House of Lords to finally remove the absolute veto of the upper house
It seemed obvious to me, within an hour of the exit poll on 8th June 2017, that it would not be possible to deliver Brexit as a purely party issue. Yet that has remained the official plan for a majority-less government