The Archbishop of Canterbury Justin Welby, has voiced his opposition to equal rights for gay couples to adopt, and has said that the bible is “clear” that only straight, married people should have sex.

In a series of previously unpublished notes, as part of the new Archbishop’s biography, he voices his opposition to equal adoption rights for gay couples, describes sexuality as a “powerful force” and says that the bible is “clear” that gay sex is wrong.

Justin Welby, 57, was confirmed as leader of the Church of England in a ceremony at St Paul’s Cathedral on 4 February. He had previously served as the Bishop of Durham for two years.

In one article, Welby discusses former Tory Cabinet Minister Michael Portillo’s admission that he had “homosexual experiences” as a student.

Welby writes that it had no bearing on Portillo’s political career, but describes sexuality as a “powerful force” which can lead people “astray”, and writes: “The standards of expected sexual morality are clear.

“Throughout the bible it is clear that the right place for sex is only within a committed heterosexual marriage.

“Interestingly all recent research also shows that the children of such a relationship are likely (not always but often) to be happier and more stable.”

He then goes on to voice his opinion that it is possible for people to change their sexuality. In the case of Portillo, Welby criticised the media for “[talking] as though his sexuality is exactly the same now as then”.

The Archbishop voices his frustration at being branded a homophobic “European Taliban” for advocating for “traditional” views on sex.

In another of the letters, from 1999, Welby criticises the Church of England charity the Children’s Society, for its decision to lift its ban on placing children for adoption and fostering with gay couples.

He wrote of the parish laving to “review its decision to support them” in light of the change, as well as urging the charity to rethink its stance. It is now illegal for charities to discriminate against gay couples.

Another issue he addresses is Prince Harry taking marijuana. He wrote: “What a surprise, a teenager has too much to drink and tries cannabis… What is the world coming to?”

Criticising the media, he continued: “No doubt, no journalist drinks anything but water, and all have difficulty even spelling marijuana. Oh please!”

The author of the biography, Reverend Dr Andrew Ahterstone, an Oxford Academic told the Telegraph: “He speaks his mind with wonderful frankness, unencumbered by nervous press officers.”

In other documents, he warns of a crisis for the Church of England due to financial pressure and dropping numbers, and even describes a “serious questions of viability” in the next ten years.

Welby, a former oil executive, will be formally enthroned in Canterbury later this month. Some critics have noted his apparent reluctance to be involved in the equal marriage debate since he was appointed Archbishop.

The former Bishop of Durham, previously said the Church of England must have “no truck with any form of homophobia”.

Although Dr Welby has previously stated his opposition to equal marriage and the ordination of gay bishops, in a speech at Lambeth Palace, Dr Welby signalled that he was willing to engage on LGBT issues.