The Battle for the Marginals
In the United Kingdom, more than half of the parliamentary seats that make up the House of Commons are classed as 'safe'. This means that the holding party is unlikely to change. In 2015, there was an exception to this rule as the Scottish National Party managed to achieve huge swings from Labour in its Scottish heartland and overturned some mega-majorities. Usually, however, the seat changes are limited to the marginal seats or 'battleground'. These seats tend to have majorities smaller than 10 percent and are heavily targeted by the political parties. In 2017, just 70 out of 650 constituencies changed hands, in 2001 the figure was even smaller with just 30 constituencies changing hands.
169 constituencies currently have majorities smaller than 10 percent, 67 of these are held by the Conservatives, 54 by Labour, 30 by the Scottish National Party, 8 by the Liberal Democrats, 3 by Plaid Cymru, 3 by the Democratic Unionists, 3 by Sinn Fein, and 1 by an Independent.
At some elections, the result in a particular seat defines the outcome of the election, in 2015 this constituency was Nuneaton (which happens to be my neighbouring seat) and in 1992 it was Basildon.
The UK's constituency boundaries were due to be redrawn in 2018 with the number of constituencies being reduced from 650 to 600. Following the result in 2017, it is currently unclear as to whether the changes will go ahead. If a general election were to be held in the imminent future, it is likely that it would be fought on the existing constituency boundaries. This list based is on the existing boundaries and will be updated when the situation becomes clear.
These constituencies were won with majorities smaller than 10 percent in 2017.