Polling experts have warned Rishi Sunak he is running out of time to woo voters with the first ballots set to be cast in the election within days.
Postal votes will start landing on doorsteps early next week, the Electoral Commission has told The Independent.
With one in five now voting by post time is running out for the prime minister to turn around Labour’s 20-point lead in many polls.
One polling expert told Mr Sunak it was “now or not at all”.
Lord Hayward, who is also a Tory peer, said many people return their postal votes as soon as they arrive.
He added: “If the Conservatives are going to have an effect, for a fairly high proportion of voters the effect is now or not at all.”
Philip Cowley, professor of politics at Queen Mary University of London, said that the UK no longer has election day “we have election days”.
“And the problem for Rishi Sunak is around one in five votes are going to be cast at a point when his party is at least 20 points behind in many opinion polls. Which means that although we keep talking about what if the polls narrow, even if they start to narrow it is too late in terms of the one-fifth of votes that have already been cast”.
The number of people voting by post has risen dramatically in the last 20 years.
Before 2000 fewer than three per cent of voters cast their ballot by post.
Since the law was changed that year, however, the numbers have skyrocketed – and in the last three elections postal votes accounted for more than a fifth of those cast.
Research suggests those who get a postal vote are likely to be older or with a disability that significantly limits their day-to-day activities.
Marginal seats are also more likely to see higher rates of postal votes, in part because parties of all colours focus on signing their supporters up, in the knowledge postal votes are more likely to be returned.
But experts say there is not an obvious pattern of high numbers of postal votes helping one party or another.
Will Jennings, professor of political science at the University of Southampton, said: “With people voting by post already, time is very much running out for the Conservatives.
“Roughly one-in-five voters will cast their ballot by post. This means that soon a large number of people will already have voted and the campaigns won't be able to change their minds.”
The elections watchdog said postal votes would likely begin to be received early next week.
But the Electoral Commission said it did not have an estimate on how many would use postal ballots in this election, although it noted that there has been a moderate increase since 2019.
A number of factors are driving this, it said, including safety concerns arising from the Covid pandemic.
Dr Hannah Bunting, from the University of Exeter’s elections centre, said: “This being a surprise July election, there may be more people on holiday on polling day, meaning we could see an increase in postal voting if people remember to apply on time.”
Members of the public have until 5pm on 19 June to register for a postal vote.
