Scottish party leaders, candidates and activists are hitting the campaign trail for the final time before the polls open in the snap summer general election.

They will be hoping to convince undecided voters to back them ahead of voting opening at 07:00 on Thursday.

First Minister John Swinney is to tell voters on Wednesday evening that while the result of the election in England is a “foregone conclusion”, the vote in Scotland is “on a knife-edge”.

“There are seats that could be decided by only a handful of votes,” he is expected to say.

“So be certain about one thing – your vote will matter. It could make all the difference.”

The SNP returned 48 MPs at the 2019 election, with Labour holding on to just one seat, but Sir Keir Starmer’s party has high hopes of a revival north of the border.

Scottish Labour leader Anas Sarwar rejected calls for his party to back the SNP in Aberdeenshire North and Moray East – where the Labour candidate was suspended and stripped of party support – to ensure Scottish Conservative leader Douglas Ross does not win the seat.

The outgoing Tory leader announced last month he would stand instead of former MP David Duguid, who was effectively de-selected after spending time in hospital.

But Mr Sarwar said: “I am the leader of the Scottish Labour Party, I want people to vote Scottish Labour.

“Scottish Labour is invested in every part of the country, so if you want to get rid of the Tories, if you want Scottish Labour representation, if you want Scotland to be at the heart of a Labour government, then you need to vote Scottish Labour – and that’s what I’m calling on people to do.”

Scottish Tory chairman Craig Hoy said several seats across the country would be “extremely close” between his party and the SNP.

“A vote for any party other than the Scottish Conservatives – including Reform, Labour or the Liberal Democrats – just increases the chances of the SNP sneaking in by the back door,” he added.

• Who should I vote for and what are the parties promising?
• Who can I vote for in the general election?
• The dos and don’ts of voting in person
• Election poll tracker: How do the parties compare?

Meanwhile, Scottish Liberal Democrat leader Alex Cole-Hamilton warned the NHS in Scotland was “teetering on the brink”.

It came after new figures showed the number of Scots waiting four hours or more at accident and emergency is the highest since January.

While health is devolved to Holyrood, Mr Cole-Hamilton’s party has made the NHS a central pillar of its pitch to voters.

“Scottish Liberal Democrats will address the problems at both the front door and the back door of the NHS,” he said.

“We will get everyone fast access to community services, including GPs and dentists, so fewer people need to go to hospital in the first place.”

• SNP manifesto
• Scottish Labour manifesto
• Scottish Conservative manifesto
• Scottish Lib Dem manifesto
• Scottish Greens manifesto

There are 4,081,585 registered voters in Scotland. About a quarter of them – 998,863 – are postal voters.

Yet concerns have been raised about Scots receiving their postal ballots in time.

The 4 July election falls in the first full week of the school summer holidays in most parts of Scotland, with delays in receiving postal votes resulting in some Scots being left without a vote due to pre-planned overseas holidays.

In a letter to Prime Minister Rishi Sunak, First Minister John Swinney said the issues had been caused by a combination of Mr Sunak’s decision to hold the vote on an “unsuitable date”, and the timetable for elections leaving “little room” to address issues.

On Monday, Rishi Sunak’s official spokesman told reporters the prime minister did not share Mr Swinney’s concerns, adding that the UK government was working with the Electoral Commission, elections officials and the Royal Mail to resolve any issues.

UK Postal Affairs Minister Kevin Hollinrake is said to be “urgently investigating” the issue, but Royal Mail has rejected claims there is a backlog, saying the service is “not complacent”.