Norwich North, which Boris Johnson visited on Tuesday, is one of Labour’s top targets at this election.
It ranks at number seven on a list of Conservative constituencies most vulnerable to Labour, and would change hands on a swing of just 0.6%.
The seat has been held by the Tories since a by-election in 2009.
Chloe Smith won the constituency from Labour during the final year of Gordon’s Brown time as prime minister.
She has retained the seat at every subsequent general election, though in 2017 her majority was cut from 4,463 to just 507.
She won 48% of the vote in 2017, with Labour close behind on 47%.
The Liberal Democrats finished a very distant third on 3%.
Norwich North was a Labour seat from 1997 until the by-election in 2009.
Before then it had been held by the Conservatives since 1983.
Labour will be desperate to win it back at this election.
If it fails to do so, it could mean the party is on track for a bad night at the polls – especially as it came so close to winning last time.
A total of five parties have candidates in Norwich North at this election: Conservatives, Labour, Liberal Democrats, Green and the UK Independence Party.
It is one of only 44 constituencies in the UK where Ukip is standing.