Not smacked: Leo with his parents Cherie and Tony after Blair's election victory last year.

LONDON, England (CNN) -- Tony Blair has revealed that he once smacked his older children -- but has given up the practice for his youngest child, 5-year-old Leo.

BBC interviewer Kirsty Wark asked the prime minister about his discipline methods during his visit to Swindon in western England.

Blair made the frank admission in a TV question-and-answer session during his trip to promote an initiative to curb anti-social behavior. (Watch what Blair said about swift justice and his lag in achieving it -- 2:12)

Blair was asked: "Do you smack your kids? Did you?" When he failed to reply immediately, Wark asked him: "Did it cause a problem?"

Blair said: "No, I think actually, funnily enough, I'm probably different with my youngest than I was with my older ones."

Misunderstanding his reply, Wark asked him: "What, you do smack the younger one?"

Blair, whose children range in age from five to 22, replied: "No-no, no-no. It was actually the other way round but ... I think, look, this smacking ... I mean, I agree with what you just said, I think everybody actually knows the difference between smacking a kid and abusing a child.

"But I, if I can honestly say this to you -- I think the problem is when you get these really, really difficult families, it's moved a bit beyond that."

After his admission, British campaigners against smacking renewed calls Wednesday for children to be protected against all forms of physical discipline.

Mary Crowley, chief executive of the Parenting Education and Support Forum, said that children should receive exactly the same protection from the law as adults.

"The law should protect children, there should be the same protection as adults protected by the law of assault, so that if things got bad, they can actually have recourse to justice," she told BBC Breakfast TV.

Caroline Abrahams, director of policy for children's charity NCH, told the UK's Press Association: "What the prime minister said yesterday about smacking older children but not his youngest is completely consistent with what is going on in our society.

"It is a bit like the way that smoking was once viewed as acceptable but now people feel highly embarrassed about it."

Jack O'Sullivan, co-founder of the group Fathers Direct, and author of the guide "He's Having a Baby," told PA smacking was "dying out" as a means of disciplining children.

He said Blair's own experience of having smacked older children but not his youngest reflected the trend.

"There has been a huge shift in fatherhood styles in the last 25 years. In the past I think that fathers had a quite narrow experience of actually looking after their children.

"It was a notion of breadwinning and then coming home and educating and disciplining. Today men take a much broader notion of caring for children and it is quite close and intimate."

An amendment to the Children Bill outlawing the "hitting" of youngsters was rejected in the House of Commons in November 2004. The bill instead allowed mild smacking while barring any physical punishment which caused visible bruising.

Family campaigner Lynette Burrows defended parents' rights to smack children, saying the pendulum had "swung too far."

"Children need smacking ... nature teaches us all throughout our lives by a small input of pain," she told PA.

"If we do not have a small input of pain, children would never survive the first two years of their lives when they are learning to walk."

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