If this week’s tetchy exchanges between Keir Starmer and Rishi Sunak at prime minister’s questions proved one thing, it was the ability of the veteran businessman, donor and publisher Michael Ashcroft to set the political agenda.

While Starmer revelled in the publication of 10 Years to Save the West, which was written by the former prime minister Liz Truss and published this week by Ashcroft’s Biteback Publishing, Sunak wanted to focus on another Biteback book – Ashcroft’s own Red Queen?, a biography of Labour’s deputy leader, Angela Rayner.

Confronted by accusations over Rayner’s tax affairs that were prompted by Red Queen?, Starmer could not hide his irritation. “We have a billionaire prime minister and a billionaire peer, both of whose families have used schemes to avoid millions of pounds of tax, smearing a working-class woman,” he said.

Starmer’s comments have now provoked a demand for an apology from Ashcroft. But the writer and publisher could be forgiven for being quietly delighted at a political week that has been dominated by his company’s two most recent books.

“Biteback selects titles for which they believe there is likely to be a readership,” Ashcroft said. “The last few years have been challenging for small independent publishers, but I am happy to say that this year Biteback is in the black and the future looks good.”

Ashcroft was once a darling of the Conservative party. Having made billions buying and selling companies in areas as diverse as cleaning services, car auctions and office security, he began ploughing money into the party in the 1990s.

His donations and his skill at persuading others to donate saw him elevated to the Lords and appointed as first the Tories’ deputy treasurer and then its deputy chair. The political journalist Peter Oborne called him “the man who bought the Tory party”, as he used his clout and expensive polling to help shape its electoral strategy.

But after 2010, his relationship with the party leader, David Cameron, began to sour, in part because of disagreements over strategy and in part because his tax domicile in Belize was attracting negative press coverage. Those close to Ashcroft say tensions were exacerbated by Cameron’s failure to give Ashcroft a senior job in the coalition government.

Ashcroft increasingly shied away from frontline politics and focused instead on his polling and publishing interests – both of which have at times proved damaging for his former colleagues.

This week, Ashcroft released a poll showing that voters now trust Labour more than the Conservatives on every major issue, including the traditional Tory strong points of tax, Brexit and defence. The poll renewed complaints among senior Tories that Ashcroft is helping Labour by putting the results of his polls into the public domain.

Meanwhile, his books, while broadly sympathetic to Conservatives, have also caused problems for the party. In 2015, he co-wrote a biography of Cameron called Call Me Dave which contained the explosive allegation the then-prime minister had once put his “private part” into the mouth of a pig as part of an initiation during his Oxford student days.

One senior Conservative said: “He’s very loyal to people, but if they let him down, he will fuck them.”

In recent years he has written largely positive biographies of Jacob Rees-Mogg and Rishi Sunak, but a far more scathing one about Boris Johnson’s wife, Carrie, which depicted her as a powerful and sometimes manipulative figure in Downing Street.

His recent books on Keir Starmer and Angela Rayner have generally been less well sourced, often relying on secondhand testimony and contemporaneous press accounts. Nevertheless, they have both proved fruitful information sources for the Conservatives, who have highlighted Ashcroft’s revelations about Starmer’s former legal clients as well as Rayner’s living arrangements.

In a statement, Ashcroft denied that his work was tainted by political bias. “With the biographies of both Keir Starmer and Angela Rayner, I sought cooperation but was flatly refused,” he said. “Notwithstanding their unhelpful attitude, I was determined to produce fair, accurate and reasonable accounts.”

Questions also surround how much input Ashcroft himself has into the books, given his extensive other activities and his reliance on co-authors and researchers such as the journalist Miles Goslett, whom he credits as his “chief researcher” on Red Queen?.

One broadcaster said: “Ashcroft never does interviews about his books because he just doesn’t know the detail and background of what goes out under his own name.”

Ashcroft himself said, however: “My researchers and I share the responsibilities. I myself carry out many of the interviews.”

His use of researchers helps explain how he manages to write books so quickly – he has put his name to 19 books since 2019, including several about the military.

Biteback’s fast turnaround times also help, even if rapid editing sometimes gets his publishing house into trouble.

This week the publisher said it would delete a sentence in Truss’s book in which she falsely attributed to the Jewish banker Mayer Amschel Rothschild a quote about the desire to “issue and control the money of a nation”.

While Ashcroft’s political and publishing activities might have sometimes landed him in trouble, they have also brought him significant power. When asked for anecdotes about him, one leftwing figure who knows him replied: “I know him enough that I know not to tell any tales about him.”

Andrew Mitchell, the deputy foreign secretary, who has known Ashcroft for many years, said: “He is a wonderful friend and a truly terrible enemy.”

The subject of Ashcroft’s next biography – the business secretary and likely Tory leadership contender Kemi Badenoch – may want to take note.