2017- Theresa May's Gamble fails
Very similar to Hillary's failed campaign in 2016, Theresa May (C) had a big advantage early. However, critical strategic blunders made in her manifesto (campaign plan) combined with Jeremy Corbyn's (L) shrewd campaigning to the youth vote helped to eliminate May's majority in Parliament, which led to her resignation 2 years later
2015- Collapse of the Lib Dems and Rise of the Scots
The Liberal Democrats had been in coalition government with the Conservatives for 4 years and they paid price. Their vote collapsed over promises by the Lib Dems that were not met. People at first didn't believe it; including former Lib Dem leader, Paddy Ashdown who threatened to "eat his hat" if the initial polls were correct (He ate a cake like hat afterwords) On the other side, the Scottish National Party experienced a buoy in support because of the recent referendum on Scottish independence. They took seats away from Labour in Scotland, allowing the Conservatives to drive on in (and call for a Brexit referendum).
1997- Tony Blair Exorcises Labour's Demons
After 18 years in the political wilderness, Tony Blair and his transformed New Labour Party (more centralized and less socialist) takes the shattered Conservative Party to the cleaners. There is a sense of hope around this broadcast, partially because by Labour finally winning and by Blair himself, which is kind of awkward viewing this from the future.
1992- The Upset Election
The election where the polls all got it wrong. Labour was thought to be a shoo-in to form the government, and at least force a hung parliament. But as the night went on, it became clear that the Tories had snatched victory once again, leaving Labour to think "If not now, when?" Look for impressionist Rory Bremner's hilarious joke about Paddy Ashdown at 38:36
1970- A Swingin' Upset
This is my favorite election of them all to watch. It has everything involved. It is the first general election to be shown in color yet there are still old fashioned number plates. You have an old fashioned feel about it yet there is updated technology. They go to Trafalgar Square, where people are diving into the fountain. Hell, they go to a swinging nightclub at one point to interview the young folk. It is a fun time for all. And it involves what at the time was one of the biggest upsets in British electoral history, with the sitting PM, Harold Wilson (L) being beaten by Edward Heath (C), against all polls. It's really a treat to watch.