Since 1945, no British govt has secured 40% of the electorate

[mcgillianaire]

2015 - 24.4% - T
2010 - 38.5%¹ - T+LD
2005 - 21.6% - L
2001 - 24.2% - L
1997 - 30.1% - L
1992 - 32.5% - T
1987 - 31.8% - T
1983 - 30.1% - T
1979 - 33.4% - T
1974 - 28.6% - L
1974 - 29.3%² - L
1970 - 33.1%³ - T
1966 - 36.2% - L
1964 - 34.0% - L
1959 - 38.8% - T
1955 - 38.1% - T
1951 - 39.3%⁴ - T
1950 - 38.6% - L
1945 - 34.9% - L

Although one shouldn't compare apples and pears, it is worth noting that this government intends to impose a 40% win threshold on balloted strikes affecting essential public services. In addition to this, a majority of the union's members would have to participate in such an action, unlike the present situation in which there are no participation thresholds and a simple majority of balloted members is sufficient to carry out a strike. Such proposals have form on both sides of the political divide, as the then Labour government under Jim Callaghan imposed a 40% win threshold on the Scottish referendum of 1979. Even though a majority voted in favour of implementing the provisions of the Scotland Act 1978, they fell 7.1% short of the threshold. Soon afterwards the Scottish National Party withdrew its support to the government, resulting in a vote of no confidence, a general election and eighteen years in the wilderness for the Labour Party. And by how many votes did the government lose the no confidence motion to trigger the general election? Just the one (311-310).

¹ This is a combined figure for the Tories (23.5%) and Lib Dems (15.0%).
² Labour secured the most seats and formed the government, but the Tories won the popular vote.
³ The voting age was lowered from 21 to 18.
⁴ The Tories secured the most seats and formed the government, but Labour won the popular vote.