The barrister told an audience at Edinburgh International Book Festival she believed the church should be “more positive” about permitting women to use artificial birth control as a means of regulating their fertility.

A devout Catholic who encouraged her husband, Tony Blair, the former Prime Minister, to convert from Anglicanism after he left office in 2007, Mrs Blair has previously revealed that she uses contraception and that the couple’s nine-year-old son Leo was conceived at Balmoral after she neglected to pack contraceptives for a stay with the Queen.

Promoting her new book Speaking for Myself, she said: “If you look at what progress women have made in the world, one of the reasons they have been able to make progress is because they have been able to control their fertility.

“I personally don’t think there is anything wrong with that, and indeed without being able to control that I wouldn’t have been able to achieve the things that I’ve been able to do.

“I think it’s a really important issue and I would prefer it if the Catholic Church took a more positive attitude towards contraception because I think there’s a lot of difference between preventing a life coming about and actually extinguishing a life when it has come about.”

The Catholic Church in Scotland said the barrister was wrong to suggest oral contraception did not “extinguish” life. A spokesman said: “That is exactly what the morning-after pill does, while the conventional pill can potentially do the same.”

The church also argues that greater availability of contraception has led to a rise in promiscuity and underage sex.

Last year Pope Benedict XVI launched a strong defence of the 1968 Papal Letter of Human Life, a controversial document written by Pope Paul VI that set out the case against artificial birth control.

The spokesman added that the tide was turning against prioritising a career over family. He said: “Increasingly women are finding that postponing or preventing pregnancy to focus on a career leaves them unable to conceive later in life, causing many to suggest that ‘kids then career’ might be a more sensible choice than ‘career then kids’.”

The church warned of four major problems when it reaffirmed its opposition to contraception. It said that birth control caused a infidelity, a general lowering of moral standards throughout society, a lowering of respect by men towards women and the coercive use of reproductive technologies by governments. It added that the past 40 years had confirmed the fears.

The church’s spokesman did not oppose regulating fertility but recommended a natural approach rather than ingesting large doses of synthetic hormones in the form of oral contraceptives that had physical, emotional and environmental side effects.

Mrs Blair was questioned about whether the church’s position was being upheld, even in its European strongholds.

She replied: “If you look at the birth rates in France and Italy and Spain it seems as though I might not be the only devout Catholic who likes to control her fertility.”

A spokesman for the Family Planning Association said: “It’s incredibly important that women have safe and convenient access to contraception because it has a big effect on their life. It’s also important that women have the choice of all 15 methods of contraception so that they can choose what fits them and their lifestyle best.”

Mr Blair launched an inter-faith foundation and converted to Catholocism after quitting UK politics. He was discouraged from discussing religion by his Downing Street press secretary Alastair Campbell, who famously advised him: “We don’t do God.”