Hartlepool in north-east England was a key constituency in both the 2015 and 2017 elections – and could be again in 2019.
The seat was one of Ukip’s top targets in 2017, with the party hoping to overturn Labour’s small majority by wooing Brexit-supporting Labour and Conservative voters.
Ukip had done particularly well in Hartlepool at the 2015 election, coming second and winning 28% of the vote.
It believed it could do even better in 2017 – but in the event Labour held the seat comfortably, winning more than half of the vote (53%) while the Tories finished second on 34% and Ukip came a distant third on 11%.
Labour also increased its majority, from 3,024 to 7,650.
Fast forward to 2019, and it is the Brexit Party that now fancies its chances in the constituency.
Nigel Farage visited Hartlepool on Monday, where he announced that his party would not field candidates in seats being defended by the Conservatives.
But his party still plans to contest seats held by Labour – including Hartlepool, which is also a Conservative target.
The Tories need a swing of 9.2% to take Hartlepool from Labour, making it one of the party’s more ambitious targets.
And the decision by the Brexit Party to fight the seat may make the Tories’ chances of victory even harder.
Hartlepool is one of dozens of Labour seats the Conservatives are targeting at this election – but the presence on the ballot paper of the Brexit Party means these contests can’t be treated simply as two-horse races.
Might the Brexit Party end up helping Labour to hold on to these kinds of constituencies, by virtue of taking some votes away from the Conservatives?
By contrast, the absence of the Brexit Party in Conservative-held seats could help the Tories cling on in parts of the country where a party like the Liberal Democrats were hoping to benefit from a split vote.
It might also have unpredictable consequences, however, if voters are put off by the idea of a Conservative-Brexit Party pact.
Mr Farage’s announcement has made it harder to predict with any certainty how the election will unfold across the UK.
A lot might depend on the behaviour of voters who backed Leave at the 2016 referendum.
A key reason Hartlepool appealed to Ukip at the last election was the fact the area voted 69.6% Leave, which was the 13th highest Leave vote in the whole of the UK.
Whether Brexit-supporting voters choose to back the Brexit Party in this year’s election, or stick with either Labour or the Tories, could prove decisive for the result.
There is also a local factor at play in Hartlepool.
The local council is currently run by a coalition of 10 Brexit Party councillors and three Conservative councillors.
The coalition doesn’t have an overall majority on the 33-seat council, but it is the largest group, collectively outnumbering the 10 Labour councillors.
Labour has held Hartlepool continuously since the seat was created in 1974.
The presence on the ballot paper of both the Conservatives and the Brexit Party might just help Labour hold the seat for even longer.
The other prospective parliamentary candidates already chosen by their parties are Andy Hagon (Lib Dem), and Mike Hill (Labour).