Rishi Sunak told the SNP to stop trying to “lock up JK Rowling” as the party's Westminster leader pushed him on a second independence referendum.

The clash with Stephen Flynn came at a fiery Prime Minister's Questions in the Commons, where the Conservative leader was mocked over the new book by his predecessor, Liz Truss.

He was also pushed over his ambition to completely scrap National Insurance, refusing three times to say if he would pay for it by cutting funding to the NHS, increasing taxes, or slashing pensions.

READ MORE: Gordon Brown: winning indyref now would be a 'challenge'

In his questions, the SNP’s Westminster leader Stephen Flynn referenced comments from Gordon Brown who told the FT this week: "In the long run, the forces pulling Britain apart are greater than the forces holding it together, unless something is done about it.”

Mr Flynn told MPs: “A former prime minister who oversaw a financial crash before being unceremoniously tossed from office told the public the truth - and I'm not referring to that one - because on Monday, Gordon Brown told the people of these isles that the forces pulling Britain apart are greater than the forces holding it together.

“So maybe the Prime Minister can find some time this afternoon to perhaps agree with just one of his predecessors.”

Mr Sunak said that he and Mr Brown agreed “very strongly” that “Scotland would be far stronger inside the United Kingdom.”

Replying, Mr Flynn raised comments from STUC General Secretary, who told the Daily Record that independence remains “unresolved” and that it “can be a very dangerous place to end up in when you are not allowing people to express their wishes in a democratic manner.”

“So may I ask the Prime Minister, does he welcome their fusome, wholehearted and warm support of the Labour Party in denying the people of Scotland that opportunity to have a say over their own future?”

In his response, Mr Sunak referenced the Scottish Government’s new Hate Crime Act, which was opposed by Ms Rowling.

On the day it took effect, she challenged police to arrest her by misgendering a number of transwomen.

Mr Sunak said: “We did have a democratic vote on that topic. But what I would suggest to the SNP is that rather than obsessing about independence and indeed wasting time cracking down on free speech and trying to lock up JK Rowling, he should focus on what the people of Scotland actually care about; schools, hospitals, jobs and our new tax cuts.”

READ MORE: JK Rowling mocks Scotland's new hate crime legislation

In his questions, Sir Keir pushed the PM on the promise to completely do away with national insurance, forecast to cost £46bn.

"He is refusing to say where the money will come from and we’ve been trying for months to get to the bottom of this," the Labour leader told MPs. 

“He can either – this is the choice – he can either cut state pension or the NHS that national insurance funds, that’s route one. Or he can put up income tax, which one is it?”

Mr Sunak swerved the question, but told the Commons that the Tories had cut taxes.

“We’ve just cut taxes by £900 for a typical worker, we’ve delivered the biggest tax cut for businesses since the 1980s, but while we’re cutting taxes Labour is already putting them up.

“In Wales putting up taxes right now for small businesses, in Birmingham putting up council tax by 21%, in London his mayor has put up taxes by 70% and this is just a glimpse of what they’d do if they got in power, a few weeks ago he finally admitted it to The Sun, what did he say he would do? I quote, he said ‘we would put up taxes’.

“It’s always the same, higher taxes and working people paying the price.”

Sir Keir said it was Mr Sunak who had hiked taxes more than any other Chancellor or Prime Minister.

He also defended deputy leader Angela Rayner, after Mr Sunak joked about the allegations over her tax affairs, following the sale of a house a decade ago. 

The Labour leader said the “billionaire Prime Minister” was “smearing a working-class woman” while his family had “used schemes to avoid millions of pounds of tax”.