Blackpool South, visited by Jeremy Corbyn on Tuesday, is one of a number of Labour-held constituencies in north-west England that the Tories are keen to win.
Gordon Marsden has held the seat for Labour since 1997, but by a very small majority at each of the last three elections.
His majority in 2017 was just 2,523, down slightly from 2,585 in 2015. This time a swing of 3.7% would be enough for Blackpool South to change hands.
It ranks at number 28 on a list of Labour seats most vulnerable to the Tories.
Nonetheless Labour won a majority of votes cast in 2017 (just over 50%), with the Conservatives second (43%) and Ukip a distant third (4%).
Having been MP since 1997, Mr Marsden is likely to have a strong and loyal local following.
By contrast, the neighbouring seat of Blackpool North & Cleveleys is held by the Conservatives, and is a Labour target at this election.
Blackpool as an area voted 67.5% Leave in the 2016 EU referendum, the 27th highest Leave vote in the country.
The Brexit Party is planning to stand in Blackpool South, although they may have only a minor impact on what has long been an exclusively Labour-Conservative battleground.
If Blackpool South stays Labour on polling day, the Tories may have more success in picking up slightly more vulnerable Labour-held seats in the North West.
Warrington South needs a swing of 2.1% to change hands, while Crewe & Nantwich would fall to the Conservatives on a swing of just 0.1%.