The ballots are going out as the candidates to be Labour leader vie for the support of the members. Electability is sure to be one of the crucial factors as they cast their vote. Keir Starmer is widely considered the frontrunner, having won 374 nominations from constituency Labour parties (58.4%) to 163 for Rebecca Long-Bailey (25.5%) and 72 for Lisa Nandy (11.3%). But whoever is elected will struggle to win in 2024, after the party won just 203 seats in 2019. Tony Blair believes that only a complete renewal of the party will do if Labour is to win again. But the two main obstacles to victory do not require a new leader to rip up the manifesto and start again.

Some 73% of leave voters supported the Conservatives in 2019, an increase of eight points from 2017

The first major obstacle is a familiar one: Brexit. Some 73% of leave voters supported the Conservatives in 2019, an increase of eight points from 2017, mostly at the expense of Labour (down nine points). Of the 54 seats that Labour lost to the Conservatives, 52 voted leave in 2016, and most of the voters who abandoned Labour for the Tories said that they did so to get Brexit done. To form a minority government in 2024, Labour needs to win about 78 seats that the Conservatives won by less than 15 points in 2019. Of these, more than 80% voted leave in 2016. As well as winning new seats, if Labour is to have any hope of winning back those it lost in 2019, it needs to win about 25% to 30% of the vote among those who voted leave in 2016. In 2019 it won just 15%.

Starmer’s potential difficulties in winning back leave voters are immediately apparent. As a key remain campaigner and the author of Labour’s second referendum policy – which more than 80% of leave voters disapproved of – there is a distinct risk that he will prove unable to win back the Labour voters who abandoned the party to support Brexit.

According to Opinium, more leave voters already associate him with Labour’s Brexit strategy than any other candidate, and he has a negative net rating (-4 points) from leave voters in the recent Lord Ashcroft poll. In fairness, however, 46% of leave voters did not have an opinion about him. This suggests that he has an opportunity to make a good first impression with them.

Long-Bailey also has a negative net rating from leave voters in the Ashcroft poll; however, Opinium’s recent poll showed that leave voters do not associate her with Labour’s Brexit strategy, which may give her an easier run at convincing them with a popular policy programme delivered well. As with Starmer, most voters have yet to form an opinion about her.

The absence of a clear view from voters is also applicable to Nandy, but to a much more pronounced extent. Presumably because she has been a backbencher since 2016, most voters have no idea who she is. When asked in an Ashcroft poll to select a word or phrase to describe her, 77% of voters simply said “don’t know”. However, Nandy is in the unique position of having voted for Boris Johnson’s Brexit deal, which may help her in leave seats that voted for the Tories.

The second big challenge for Labour is to convince voters that the party’s polices are credible and achievable. According to the Ashcroft poll, 62% of the voters Labour lost to the Conservatives did not believe Labour would be able to deliver on its promises. It is not that voters did not approve of Labour’s policies – indeed, those policies are overwhelmingly supported by the public – but that they did not see them as achievable.

Starmer’s supporters would likely argue that his experience as shadow Brexit secretary has given him a forensic grasp of policy, which would help him to explain Labour’s policies better while giving them an “electable” face. Indeed, as of right now, Starmer has the best approval ratings with voters – with a net +5 points, according to Ipsos Mori, and +15 points, according to Lord Ashcroft. However, the proportion of “don’t knows” in these polls is very high (51%, according to Ashcroft), so these early polls may change.

Nandy, meanwhile, has urged Labour to abandon some policies, such as free broadband, that she sees as not being credible with the voters. It is certainly true that free broadband was the 2019 policy with the lowest net approval in a DeltaPollUK poll. However, Nandy’s desire to also abandon Labour’s plans of mass nationalisation and abolishing tuition fees may be a misstep: the voters overwhelmingly support those policies.

Finally, Long-Bailey’s supporters would likely argue that as the author of many Labour policies, she is best placed to explain them. Indeed she is already associated with Labour’s manifesto and with its policies of nationalisation. However, her approval ratings with voters are currently the lowest of any candidate (-16 points according to Ipsos Mori, and -20 points according to Ashcroft). As with Starmer and Nandy, the proportion of “don’t knows” are very high, but this nonetheless indicates that Long-Bailey will have to improve her image with the voters if she wins.

To win back leave voters and convince all voters that Labour’s policies are achievable is no easy task. There is no candidate who ticks all the boxes, so Labour members face a difficult choice. But whoever is elected will face the same challenges, and they will need the support of the whole Labour party to succeed. Uniting the party behind the leader will give them the best chance. Those of us who want a Labour victory in 2024 can only hope that whoever wins will be up to the task.

• Ell Smith is the founder of Stats for Lefties, a blog and podcast that examines polls and elections