An influential conservative cardinal has established himself as a “parallel authority” to Pope Francis, according to a new book that depicts the pontiff as a prophetic reformer who is surrounded by opponents waging “guerrilla warfare” against him.

Cardinal Robert Sarah, a prelate from Guinea who heads the Vatican’s liturgy department, has sought to present an alternative leadership model for the global Roman Catholic church, Christopher Lamb claims in The Outsider.

“Cardinal Sarah has established himself as a ‘parallel’ authority to Francis, through his books, lectures, and frequent travel to conservative outposts,” writes Lamb, Vatican correspondent for Catholic weekly magazine The Tablet for the past five years.

The controversial book written by Cardinal Sarah with Pope Emeritus Benedict ‘combines a mystical spirituality with an unbending defence of traditional Catholic teaching’.

“He does not directly confront or criticise the pope but [presents] an alternative leadership model for the church. Privately, he listens to the complaints about Francis; he shares some of the concerns, although is very careful in what he says. He doesn’t support the attacks, but neither does he do anything to stop them.”

Sarah, who is frequently tipped as a potential successor to Francis, “combines a mystical spirituality with an unbending defence of traditional Catholic teaching. Were he elected pope, he would undoubtedly harken back to Pius XII, a neo-traditionalist who would ‘reign’ as pope rather than adopt the style of the Latin American [Francis], who rolls up his sleeves and takes risks to take the church out on to the street.”

The cardinal is described as “extraordinarily conservative” and “very uncomfortable” with women holding positions of authority in the church’s charitable network.

In January, Sarah co-authored, with the retired Pope Benedict a book called From the Depths of our Hearts, defending clerical celibacy just as Francis was considering easing that rule in the Amazon, where there is a shortage of priests. The book was seen as a challenge to Francis’s authority. He eventually decided against opening up the priesthood to married men.

Sarah has “developed a loyal following in conservative circles, particularly in the United States”, according to Lamb. .

Sarah has denied he is an opponent of Francis. “I am loyal to the pope. They cannot quote a word, a phrase, a gesture in which I oppose the pope, it is ridiculous,” he said last year. His spokesperson did not respond to the Observer’s request for comment.

Lamb’s book cites more than 100 instances of attacks on Francis’s papacy. Opposition to Francis is not just theological, but political, he writes. “Some in the church have entered into alliances with political figures, such as Steve Bannon, President Donald Trump’s former chief strategist, and Matteo Salvini, Italy’s [former] deputy prime minister, to try and thwart the pope. Francis, who has repeatedly urged the world to build bridges rather than walls, to push for dialogue and unity instead of division, has become a prime target for supporters of the Trumpian, populist politics gaining traction across Europe.”

According to Lamb, US Catholic donors have cut off funding under Francis, furious at their loss of influence and in protest at the pope’s pronouncements on capitalism, the environment, refugees and inequality.

“No one can buy their way into one of Francis’s masses … You are more likely to hear mass celebrated by the pope if you are a Vatican gardener than if you have donated millions.”

According to Lamb, “everyone agrees, whether they are on the so-called conservative or liberal end of the spectrum, that the open opposition against [Francis] has not been seen in centuries, if ever … Worldly and clerical establishments, whether from Donald Trump and Fox News to conservative cardinals and an influential Catholic media network, have been engaged in guerrilla warfare against this pontificate.”