Boris Johnson "thinks about religion a lot" but does not actively practise any faith, he has revealed.

The Telegraph quotes Johnson as saying he is not a "serious practising Christian" and it would be "pretentious" to suggest otherwise.

The Mayor of London, and likely future candidate for leader of the Conservative Party, has in the past indicated that his faith wavers – like the reception for Magic FM in the Chilterns.

David Cameron has used the same line, describing himself as "a sort of typical member of the Church of England... We are racked with doubts, but sort of fundamentally believe, but don't sort of wear it on our sleeves or make too much of it. I think that is sort of where I am."

However, Cameron has also described Britain as a "Christian country", and told a group of church leaders last year that he finds his "moments of greatest peace" when he attends the sung Eucharist at St Mary Abbots in Kensington every other Thursday. He has also suggested that politicians should be inspired by Christianity.

"Greater confidence in our Christianity can also inspire a stronger belief in our work as politicians to get out there and make a difference to people's lives – and it should inspire our support for churches and faith organisations in the vital work they do in our society and around the world," he wrote in the foreword to the programme for the National Parliamentary Breakfast last year.

"Whatever our political parties and whatever our disagreements these are values we share."

Johnson has faced criticism today for describing British jihadis as "literally w***ers" who "are not making it with girls and so they turn to other forms of spiritual comfort".

In an interview with the Sun, Johnson said those who join groups such as ISIS "are just young men in desperate need of self-esteem who do not have a particular mission in life, who feel that they are losers and this thing makes them feel strong – like winners."

They are "very badly adjusted in their relations with women" he added, but was later forced to defend the comments.

"The crucial thing is that these are young men, principally young men who are growing up without much sense of success in their lives, without a feeling that the world holds much for them and...their problems need addressing in all sorts of ways," he told Sky News.