I was going to write this after the recent UK election a few months ago but didn't get a chance to. But after watching a lot of BBC political documentaries on You Tube, I've come to the conclusion what happened was the end of an era which lasted from 1979 until 2015, an era in which both major parties of British politics, Labour and Conservative mirrored each other in their experiences as parties both in and out of power. Both parties were in power for long stretches of time (Conservative 1979-1997) and Labour (1997-2010 although the Tories went 18 years like Labour without a majority) and both parties went through painful "wilderness" years which brought about gut-wrenching change to both of them. In fact, both parties were such mirror images of each other, you could even line-up some of the politicians involved and they would compared very nicely with each other. For example:
1). Tony Blair = David Cameron (The PMs who were the party modernizers)
2). Tony Benn = Margaret Thatcher (Ideologues with adoring fans who tried to give their respective parties purpose and ideas but also were very divisive figures)
3). Michael Foot = Ian Duncan Smith (Good studies in what happens to organizations when people not suited for leadership lead them)
4). Denis Healey = Kenneth Clarke (The respective best leaders neither party ever had)
5). John Smith = Michael Howard (Transitory figures to the party modernizers)
6). Neil Kinnock = William Hague (Opposition leaders in difficult times for their respective parties)
7). Jim Callaghan = John Major (You can make the case for comparing Gordon Brown with Major but the deep splits in both parties during their wilderness years began with both men's PM tenures)
8). Gordon Brown = Michael Heseltine (Important party figures trying to plot their way to the top with Brown ultimately making it but soon crashing and burning. Only Heseltine's health kept him from being Conservative leader.
9). Robin Cook = Geoffery Howe (Men of conscious resigning in the wake of policy differences)
10). Roy Hattersley = Michael Portillo (Not a neat comparison but not exactly loyal deputy leaders)
There's also some corresponding events as well. Black Wednesday (1992) = The Panic of 2008. The Winter of Discontent = The Poll Tax. The ouster of Margaret Thatcher in 1990 via parliamentary coup and the near coup by Gordon Brown against Tony Blair in 2007 and subsequent leadership elections as well.
There are others I'm sure you could make on a cabinet level but you get the picture. The rise of the SNP has basically ended one era of British politics and now we're in a new era that will need its own story to be told 15-20 years down the road.