Parents need practical support for bringing up their children rather than tax incentives to get married, Education Secretary Alan Johnson has said.
He insisted children's upbringing was more important than their parents' marital status as Tony Blair said a minority of problem families needed targeted intervention.
Mr Johnson dismissed Tory leader David Cameron's call for the re-introduction of tax breaks for married couples, saying relationships relied on love rather than money. "It's the child that is at the centre of this, it's the parenting that matters, it's not the form of the relationship," he told GMTV.
"It's wrong for politicians to suggest that if we say everyone should be married, they're suddenly going to go out and get married. It's wrong to suggest that tax and legislation makes relationships, it's not, it's love," he added.
Mr Johnson, who was brought up by his sister after being orphaned at the age of 12, said he found the Tory leader's approach to the issue "strange".
Mr Blair denied later that the argument about "marriage versus lone parents" would address Britain's gun and gang culture.
Speaking at his monthly Downing Street press conference, he said the problems ran "far, far deeper" than broken homes.
There was a hard core of problem families who were a "special case" and had to be dealt with differently, he said.
"Their problems are so intense and so profound and they are so shut out from the normal way of living in our society that unless you are prepared to intervene at a very early stage ... you are not going to deal with it," Mr Blair said.
Mr Johnson is due to add, in a speech to relationship organisation Relate, that marriage "represents the pinnacle of a strong relationship". But he will add: "That does not mean that all children from married couples fare well, nor that every other kind of alternate family structure is irretrievably doomed to fail. Our family policy must be bias-free."
