The SNP has won three key seats but its hopes of securing an overall majority in the Scottish Parliament election remain on a knife edge.

The party has taken both Edinburgh Central – where former MP Angus Robertson was standing for the SNP – and Ayr from the Conservatives.

It also won the East Lothian seat from Labour.

But it fell short in other targets, with counting in the remaining seats due to resume on Saturday.

No other constituencies have changed hands so far, with the SNP currently on 39 seats, the Liberal Democrats four, Tories two and Labour one.

But the opposition parties will see their number of seats increase dramatically once the regional list results are finalised on Saturday.

Polling expert Prof Sir John Curtice said it was now unlikely, but not impossible, that the SNP would achieve an overall majority in the new Holyrood parliament.

And he said there were clear signs that tactical voting by pro-UK voters in some parts of the country had been successful.

The Alba Party, which was founded by former first minister and SNP leader Alex Salmond, looks unlikely to win any seats.

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As the count resumed on Saturday, Aberdeenshire East was first to declare with the SNP’s Gillian Martin holding her seat with a reduced majority of 1,889 over the Scottish Conservatives – who increased their vote share by 11%.

Friday’s results included First Minister Nicola Sturgeon – the SNP leader – easily holding off a challenge from Scottish Labour leader Anas Sarwar in her Glasgow Southside constituency.

Ms Sturgeon won by 9,456 votes, only marginally lower than the 9,593 she won by in 2016.

Turnout has been higher than anticipated in many areas, with the SNP’s share of the vote falling in many of the early constituencies to declare but increasing in others.

Ms Sturgeon said that the SNP “appears to be on course for a fourth consecutive election victory and to be on course to have the privilege of forming a government again”.

She pledged to “get back to work immediately” and lead the country’s Covid recovery.

“And then, when the time is right, to offer this country the choice of a better future,” she added.

It comes as UK Prime Minister Boris Johnson suggested he would reject any calls for a second independence referendum, saying it would be “irresponsible and reckless” right now.

Asked if an SNP majority would mean there was a mandate for another vote, he told the Daily Telegraph: “I think that count is still taking place and we’ll have to see what happens. I listened to the Scottish election carefully. My impression was that they [the SNP] moved away from the idea of a referendum, and I think very wisely.

“I don’t think this is anything like the time to have more constitutional wrangling, to be talking about ripping our country apart, when actually people want to heal our economy and bounce forward together. That’s what people want.”

However deputy first minister John Swinney told BBC Breakfast that his party would legislate for a second referendum if Mr Johnson were to block one.

He said: “We’ve said we will take forward legislation to have a legal referendum – we already have put in place some of the legislative arrangements for that process. We will embark on such an agenda should there be a majority for such a proposition in the Scottish Parliament.”

Mr Swinney said that although he was waiting to see the “electoral arithmetic” of the final results, he was “very confident” there would be a majority of candidates “elected on a programme to deliver a referendum on independence”.

This election has a long way to go with a further 26 constituencies and all 56 regional list seats still to declare.

While the SNP is on course to finish as the largest party, there are only limited opportunities left for them to do so with an overall majority.

To achieve that they really need to hold all they have and pick up an additional constituency seat like Aberdeenshire West, where the Conservatives are defending a majority of 900 votes.

There is also a possible pathway if they do better than expected on the regional lists which are very hard to predict because of the proportional voting system.

If the SNP fall short of that outright majority they could enter a fourth term in office as a minority government (as they are now) or seek a more formal arrangement with another party – most likely the Greens.

Together the SNP and the Greens will almost certainly have a pro-independence majority at Holyrood – committed to holding another referendum that the UK government seems determined to resist.

A big wrangle over indyref2 is coming and it could end up in the UK Supreme Court.

The constituencies that declared on Friday included eight of the SNP’s top 10 target seats.

The Conservatives held Dumfriesshire, which had been one of the SNP’s goals, with Oliver Mundell increasing his majority, while Jackson Carlaw held the marginal Eastwood seat for the Tories from the SNP.

And Labour’s Daniel Johnson held off the SNP challenge in Edinburgh Southern and the party’s deputy leader Jackie Baillie increased her majority over the SNP in Dumbarton.

The election is seen as being crucial to the future of the UK as the result could impact on whether or not there is a second referendum on Scottish independence.

The SNP – which has formed the devolved Scottish government since 2007 – will once again finish as the largest party, but is seeking to win an overall majority to strengthen the case for indyref2.

Although it is not yet clear that it will win a majority by itself, there is likely to be a pro-independence majority in the parliament once the Scottish Greens are allocated regional list seats on Saturday.

The coronavirus pandemic meant that traditional overnight counting was impossible, with the results instead being announced over the course of Friday and Saturday.

A record number of people had already cast their ballots by post before the polls opened on Thursday morning – with more than a million having registered for postal ballots.

Other elections also took place across the UK on Thursday, including for the Welsh Parliament, 143 English councils and 13 local mayors, as well as a by-election for the Westminster seat of Hartlepool in the north east of England – which was won by the Conservatives from Labour.

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