Starmer has been in charge of the party for over a year, and supporters will be expecting him to start making inroads following Labour’s defeat in 2019’s general election.
However, since the turn of the year, national polls have consistently shown the Conservatives ahead – although there was some tightening over the weekend, suggesting charges of Tory “sleaze” over cronyism and the funding of Boris Johnson’s flat refurbishment may be beginning to cut through.
Watch: Sir Keir Starmer admits Labour has 'mountain to climb'
But another opinion poll has showed the Tories opening up a double-digit lead in the Hartlepool by-election race, which is taking place on the same day as the council elections in England.
Ahead of Thursday’s vote, the Survation poll for ITV’s Good Morning Britain put the Conservatives on 50% – 17 points ahead of Labour, in a seat that has been red since it was created in 1974.
Starmer has visited the constituency three times in the course of the by-election, and said he is battling for every vote as he hopes Labour will not lose another seat in the party’s “red wall”.
Defeat in Hartlepool – which Labour held with a majority of 3,595 in 2019, even as other bricks in the red wall crumbled – would be a blow to his leadership.
Speaking to reporters on the campaign trail in St Asaph, north Wales, Starmer said: “The task I took on as leader of the Labour Party was to rebuild, out of the worst general election result since 1935, and put the Labour Party back in a position to win the next general election.
“And that’s a mountain to climb. We’re climbing that mountain, it has taken difficult decisions, and I’m absolutely up for any further difficult decisions there will be.”
With voting taking place across Great Britain on Thursday – including for English councils, the Scottish Parliament and the Welsh Senedd – Starmer acknowledged he is facing his first major electoral test and promised to take “full responsibility” for the results.
Meanwhile, Labour sources told The Guardian the party was in danger of losing control of Sunderland City Council and Durham County Council for the first time in 50 years.
Watch: Starmer 'fighting for every vote' in Hartlepool by-election