Boris Johnson has again rejected calls for a second vote on Scottish independence as he said Covid-19 has shown the UK as a “fantastically strong institution”.

The Prime Minister, on a visit to Orkney, said the strength of the UK has been critical in the response to coronavirus.

He also spoke of his desire to “build back better” after the pandemic.

The Prime Minister’s visit comes after support for Scottish independence reached a record high of 54% in an opinion poll earlier this month.

Mr Johnson said: “The union is a fantastically strong institution, it’s helped our country through thick and thin, it’s very, very valuable in terms of the support we’ve been able to give to everybody throughout all corners of the UK.”

First Minister Nicola Sturgeon argued his visit – the day before Mr Johnson marks one year in charge at Downing Street – highlights a key argument for independence.

She tweeted: “I welcome the PM to Scotland today. One of the key arguments for independence is the ability of Scotland to take our own decisions, rather than having our future decided by politicians we didn’t vote for, taking us down a path we haven’t chosen. His presence highlights that.”

While she welcomed financial support from Westminster, she said it is “not some kind of favour” to Scots.

“Let’s be clear, this is borrowed money and the reason it is coming to the Scottish Government from the UK Government is the UK Government holds the borrowing powers that Scotland doesn’t hold,” she said.

“Scottish taxpayers will pay the cost of that borrowing in the same way as taxpayers across the UK will so it is not some kind of favour that is being done for Scotland.

“And if the Scottish Government held the borrowing powers we would be able to provide that support directly, and perhaps we would be able to have greater flexibility in how we design these schemes.”

Saying no one should be “championing and celebrating a pandemic that has taken thousands of lives as some example of the pre-existing political cases we want to make”, she added: “Campaigning right now is not my priority. Boris Johnson has every right to be on a campaign visit but in his shoes it’s not what I would do.”

Ms Sturgeon spoke out after the Prime Minister argued there should not be another independence referendum – even if the SNP win a majority of seats at next May’s Holyrood elections, as polls indicate they could do.

Mr Johnson said: “We had a referendum on breaking up the union a few years ago, I think only six years ago, that is not a generation by any computation and I think what people really want to do is see our whole country coming back strongly together and that’s what we’re going to do.

“What we’ve seen throughout this crisis is the importance of the strength of the union in dealing with certain crucial, crucial things – supporting people through the furlough scheme, the work of the Army and armed services in testing and moving people around.

“Now, through Barnett consequences, we’ve put another £250 million into the NHS in Scotland to make sure that we’re ready for the winter because we’ve got to be clear that this thing has not gone away.”

He added: “Throughout the UK we’ve done very well in getting coronavirus under control but it is not the end of the story and we’ve got to be very, very vigilant as we go forward into the colder months and that’s why we’re supporting the NHS with extra cash.

“I think that the merits of the union are very, very strong – they’ve been proved throughout this crisis.

“What we want to do now – and this is why I’m here in Orkney – is to show how we can, not just deal with the health crisis, but work to deal with the economic consequences together, building back better, investing in green technology and a green recovery.”

During his first stop at Copland Dock, Stromness, Mr Johnson heard from crab fishermen about the challenges the fishing industry faces and cited the role of the UK Government’s efforts to protecting jobs during the coronavirus pandemic.

‎Karl Adamson, the Orkney Fishermen’s Society’s live shellfish manager, revealed he spoke to the Prime Minister about reopening access to the lucrative Chinese market – an issue Mr Johnson said he would take up on his return to Westminster.

“Some help from the top of the UK Government would go a long way,” Mr Adamson said, adding “the situation of not being able to sell directly to China is very difficult, to put it mildly”.

The visit comes as the UK and Scottish Governments announced they will both contribute £50 million to a £100 million growth deal for the Northern and Western Isles.

Mr Johnson hailed this as a “real opportunity for people here to get some funding to increase what they are already doing, amazing new green technology”.

He later visited RAF Lossiemouth in Moray where he met service personnel and their families.

Questioned if he was politicising the coronavirus crisis, he said “of course not, no”.