Derbyshire North East, which Jeremy Corbyn visited on Monday, is one of half a dozen Conservative constituencies in the East Midlands that Labour is targeting in this election.
It used to be one of Labour’s safest seats in the region, and was held by the party continuously from 1935 until 2017.
Then Lee Rowley won it for the Conservatives on a swing of nearly 5%.
Labour’s majority in the seat had dwindled since the 2010 general election, so victory for the Tories in 2017 was not unexpected.
But Mr Rowley is defending a majority of only 2,861, and Labour would need a swing of just under 3% to defeat him.
This is the sort of constituency Labour has to win if it wants to become the largest party in a hung parliament – never mind forming a majority government.
If it manages to take Derbyshire North East, Labour could be in line to pick up other Tory-held marginal seats in the East Midlands, such as Mansfield, Corby and Loughborough.
Alternatively, the party could under-perform in the region and fail to make any gains, besides losing seats to the Conservatives such as Ashfield and Lincoln.
Both Mr Corbyn and Boris Johnson have visited the region during the campaign – and would be wise to do so again.
Four parties are standing in Derbyshire North East at this election: Conservatives, Labour, Liberal Democrats and Green.