This graph shows the UK-wide vote shares for each of the three main parties, along with the total Conservative plus Labour share. As you can see, the proportion of people voting for one of the two largest parties dropped again this time, hitting another record post-war low.
The combination of this and our voting system means that the Conservative Party’s share of the vote was sufficient to make the party the largest, but at any previous election it would have been a vote share that would have sent the party to defeat rather than 10 Downing Street. The Liberal Democrat vote share was the party’s second best since the war whilst Labour’s was its second worst.
UPDATE: To see how turnout has also varied and had an impact on the votes won by parties, see my second general election vote shares graph.